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 $102.98   4.673%   $107.7923   $107.79   $107.80   $107.80  
  Purchase #2 $177.39   9.573%   $194.3715   $194.37   $194.35   $194.40  
  Purchase #3 $173.81   12.738%   $195.9499   $195.95   $195.95   $195.90  
  Purchase #4 $239.79   12.553%   $269.8908   $269.89   $269.90   $269.90  
  Purchase #5 $10.32   12.797%   $11.6407   $11.64   $11.65   $11.60  
  Purchase #6 $181.40   9.717%   $199.0266   $199.03   $199.05   $199.00  
  Purchase #7 $53.68   6.774%   $57.3163   $57.32   $57.30   $57.30  
  7 purchase totals = $939.37       $1,035.9881   $1,035.99   $1,036.00   $1,035.90