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 $48.33   10.158%   $53.2394   $53.24   $53.25   $53.20  
  Purchase #2 $55.36   7.812%   $59.6847   $59.68   $59.70   $59.70  
  Purchase #3 $170.48   6.281%   $181.1878   $181.19   $181.20   $181.20  
  Purchase #4 $169.97   6.853%   $181.618   $181.62   $181.60   $181.60  
  Purchase #5 $171.89   3.600%   $178.078   $178.08   $178.10   $178.10  
  Purchase #6 $136.37   11.603%   $152.193   $152.19   $152.20   $152.20  
  Purchase #7 $68.77   11.824%   $76.9014   $76.90   $76.90   $76.90  
  7 purchase totals = $821.17       $882.9023   $882.90   $882.95   $882.90