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 $246.54   8.292%   $266.9831   $266.98   $267.00   $267.00  
  Purchase #2 $148.27   4.735%   $155.2906   $155.29   $155.30   $155.30  
  Purchase #3 $219.82   4.500%   $229.7119   $229.71   $229.70   $229.70  
  Purchase #4 $188.38   11.219%   $209.5144   $209.51   $209.50   $209.50  
  Purchase #5 $82.83   13.803%   $94.263   $94.26   $94.25   $94.30  
  Purchase #6 $156.45   11.759%   $174.847   $174.85   $174.85   $174.80  
  Purchase #7 $89.97   8.387%   $97.5158   $97.52   $97.50   $97.50  
  7 purchase totals = $1,132.26       $1,228.1258   $1,228.12   $1,228.10   $1,228.10