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 $84.87   10.229%   $93.5514   $93.55   $93.55   $93.60  
  Purchase #2 $46.97   3.683%   $48.6999   $48.70   $48.70   $48.70  
  Purchase #3 $108.39   11.322%   $120.6619   $120.66   $120.65   $120.70  
  Purchase #4 $214.63   8.640%   $233.174   $233.17   $233.15   $233.20  
  Purchase #5 $62.93   10.149%   $69.3168   $69.32   $69.30   $69.30  
  Purchase #6 $153.82   12.644%   $173.269   $173.27   $173.25   $173.30  
  Purchase #7 $156.37   8.302%   $169.3518   $169.35   $169.35   $169.40  
  7 purchase totals = $827.98       $908.0248   $908.02   $907.95   $908.20