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 $216.56   10.341%   $238.9545   $238.95   $238.95   $239.00  
  Purchase #2 $88.93   7.209%   $95.341   $95.34   $95.35   $95.30  
  Purchase #3 $206.50   8.568%   $224.1929   $224.19   $224.20   $224.20  
  Purchase #4 $224.37   10.555%   $248.0523   $248.05   $248.05   $248.10  
  Purchase #5 $182.72   3.629%   $189.3509   $189.35   $189.35   $189.40  
  Purchase #6 $39.53   5.571%   $41.7322   $41.73   $41.75   $41.70  
  Purchase #7 $148.86   12.173%   $166.9807   $166.98   $167.00   $167.00  
  7 purchase totals = $1,107.47       $1,204.6045   $1,204.59   $1,204.65   $1,204.70