Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $219.35   12.388%   $246.5231   $246.52   $246.50   $246.50  
  Purchase #2 $169.29   10.432%   $186.9503   $186.95   $186.95   $187.00  
  Purchase #3 $176.60   11.628%   $197.135   $197.14   $197.15   $197.10  
  Purchase #4 $235.54   5.457%   $248.3934   $248.39   $248.40   $248.40  
  Purchase #5 $153.80   10.275%   $169.603   $169.60   $169.60   $169.60  
  Purchase #6 $130.36   6.550%   $138.8986   $138.90   $138.90   $138.90  
  Purchase #7 $180.28   11.378%   $200.7923   $200.79   $200.80   $200.80  
  7 purchase totals = $1,265.22       $1,388.2957   $1,388.29   $1,388.30   $1,388.30