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 $78.84   9.554%   $86.3724   $86.37   $86.35   $86.40  
  Purchase #2 $239.43   7.694%   $257.8517   $257.85   $257.85   $257.90  
  Purchase #3 $88.56   6.154%   $94.01   $94.01   $94.00   $94.00  
  Purchase #4 $113.26   11.699%   $126.5103   $126.51   $126.50   $126.50  
  Purchase #5 $54.74   8.209%   $59.2336   $59.23   $59.25   $59.20  
  Purchase #6 $202.46   6.336%   $215.2879   $215.29   $215.30   $215.30  
  Purchase #7 $50.29   5.792%   $53.2028   $53.20   $53.20   $53.20  
  7 purchase totals = $827.58       $892.4687   $892.46   $892.45   $892.50