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 $50.42   11.506%   $56.2213   $56.22   $56.20   $56.20  
  Purchase #2 $135.51   8.869%   $147.5284   $147.53   $147.55   $147.50  
  Purchase #3 $125.69   10.171%   $138.4739   $138.47   $138.45   $138.50  
  Purchase #4 $64.71   5.296%   $68.137   $68.14   $68.15   $68.10  
  Purchase #5 $211.58   6.405%   $225.1317   $225.13   $225.15   $225.10  
  Purchase #6 $117.44   9.839%   $128.9949   $128.99   $129.00   $129.00  
  Purchase #7 $171.35   11.152%   $190.459   $190.46   $190.45   $190.50  
  7 purchase totals = $876.70       $954.9462   $954.94   $954.95   $954.90