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 $129.88   5.821%   $137.4403   $137.44   $137.45   $137.40  
  Purchase #2 $36.31   13.808%   $41.3237   $41.32   $41.30   $41.30  
  Purchase #3 $206.98   8.217%   $223.9875   $223.99   $224.00   $224.00  
  Purchase #4 $232.50   6.656%   $247.9752   $247.98   $248.00   $248.00  
  Purchase #5 $41.48   13.377%   $47.0288   $47.03   $47.05   $47.00  
  Purchase #6 $194.55   4.812%   $203.9117   $203.91   $203.90   $203.90  
  Purchase #7 $181.61   6.617%   $193.6271   $193.63   $193.65   $193.60  
  7 purchase totals = $1,023.31       $1,095.2943   $1,095.30   $1,095.35   $1,095.20