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 $216.34   12.133%   $242.5885   $242.59   $242.60   $242.60  
  Purchase #2 $220.46   13.161%   $249.4747   $249.47   $249.45   $249.50  
  Purchase #3 $85.53   13.386%   $96.979   $96.98   $97.00   $97.00  
  Purchase #4 $162.77   12.570%   $183.2302   $183.23   $183.25   $183.20  
  Purchase #5 $161.82   9.581%   $177.324   $177.32   $177.30   $177.30  
  Purchase #6 $155.65   9.190%   $169.9542   $169.95   $169.95   $170.00  
  Purchase #7 $41.44   11.190%   $46.0771   $46.08   $46.10   $46.10  
  7 purchase totals = $1,044.01       $1,165.6277   $1,165.62   $1,165.65   $1,165.70