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 $113.97   3.116%   $117.5213   $117.52   $117.50   $117.50  
  Purchase #2 $235.53   4.581%   $246.3196   $246.32   $246.30   $246.30  
  Purchase #3 $133.48   5.299%   $140.5531   $140.55   $140.55   $140.60  
  Purchase #4 $180.68   3.648%   $187.2712   $187.27   $187.25   $187.30  
  Purchase #5 $59.99   3.317%   $61.9799   $61.98   $62.00   $62.00  
  Purchase #6 $119.72   11.285%   $133.2304   $133.23   $133.25   $133.20  
  Purchase #7 $69.30   13.415%   $78.5966   $78.60   $78.60   $78.60  
  7 purchase totals = $912.67       $965.4721   $965.47   $965.45   $965.50