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 $105.62   7.309%   $113.3398   $113.34   $113.35   $113.30  
  Purchase #2 $217.33   11.171%   $241.6079   $241.61   $241.60   $241.60  
  Purchase #3 $250.86   5.457%   $264.5494   $264.55   $264.55   $264.50  
  Purchase #4 $116.79   5.569%   $123.294   $123.29   $123.30   $123.30  
  Purchase #5 $159.45   10.803%   $176.6754   $176.68   $176.70   $176.70  
  Purchase #6 $22.95   13.132%   $25.9638   $25.96   $25.95   $26.00  
  Purchase #7 $59.78   8.269%   $64.7232   $64.72   $64.70   $64.70  
  7 purchase totals = $932.78       $1,010.1535   $1,010.15   $1,010.15   $1,010.10