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 $205.26   3.280%   $211.9925   $211.99   $212.00   $212.00  
  Purchase #2 $131.30   10.185%   $144.6729   $144.67   $144.65   $144.70  
  Purchase #3 $46.26   11.264%   $51.4707   $51.47   $51.45   $51.50  
  Purchase #4 $42.69   12.741%   $48.1291   $48.13   $48.15   $48.10  
  Purchase #5 $229.33   3.611%   $237.6111   $237.61   $237.60   $237.60  
  Purchase #6 $57.59   7.819%   $62.093   $62.09   $62.10   $62.10  
  Purchase #7 $238.34   9.293%   $260.4889   $260.49   $260.50   $260.50  
  7 purchase totals = $950.77       $1,016.4582   $1,016.45   $1,016.45   $1,016.50