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 $76.78   10.635%   $84.9456   $84.95   $84.95   $84.90  
  Purchase #2 $59.88   3.483%   $61.9656   $61.97   $61.95   $62.00  
  Purchase #3 $98.91   9.650%   $108.4548   $108.45   $108.45   $108.50  
  Purchase #4 $203.51   4.322%   $212.3057   $212.31   $212.30   $212.30  
  Purchase #5 $61.42   4.248%   $64.0291   $64.03   $64.05   $64.00  
  Purchase #6 $9.54   11.425%   $10.6299   $10.63   $10.65   $10.60  
  Purchase #7 $221.76   12.421%   $249.3048   $249.30   $249.30   $249.30  
  7 purchase totals = $731.80       $791.6355   $791.64   $791.65   $791.60