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 $34.30   5.849%   $36.3062   $36.31   $36.30   $36.30  
  Purchase #2 $100.61   13.534%   $114.2266   $114.23   $114.25   $114.20  
  Purchase #3 $204.29   9.341%   $223.3727   $223.37   $223.35   $223.40  
  Purchase #4 $60.36   13.548%   $68.5376   $68.54   $68.55   $68.50  
  Purchase #5 $187.72   6.256%   $199.4638   $199.46   $199.45   $199.50  
  Purchase #6 $129.82   10.228%   $143.098   $143.10   $143.10   $143.10  
  Purchase #7 $55.60   7.824%   $59.9501   $59.95   $59.95   $60.00  
  7 purchase totals = $772.70       $844.9550   $844.96   $844.95   $845.00