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 $192.76   10.290%   $212.595   $212.60   $212.60   $212.60  
  Purchase #2 $46.56   3.180%   $48.0406   $48.04   $48.05   $48.00  
  Purchase #3 $63.55   7.757%   $68.4796   $68.48   $68.50   $68.50  
  Purchase #4 $184.85   6.369%   $196.6231   $196.62   $196.60   $196.60  
  Purchase #5 $13.56   5.425%   $14.2956   $14.30   $14.30   $14.30  
  Purchase #6 $154.48   8.779%   $168.0418   $168.04   $168.05   $168.00  
  Purchase #7 $52.48   10.735%   $58.1137   $58.11   $58.10   $58.10  
  7 purchase totals = $708.24       $766.1894   $766.19   $766.20   $766.10