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 $188.25   12.596%   $211.962   $211.96   $211.95   $212.00  
  Purchase #2 $176.62   4.704%   $184.9282   $184.93   $184.95   $184.90  
  Purchase #3 $62.52   6.508%   $66.5888   $66.59   $66.60   $66.60  
  Purchase #4 $113.68   6.727%   $121.3273   $121.33   $121.35   $121.30  
  Purchase #5 $59.83   8.592%   $64.9706   $64.97   $64.95   $65.00  
  Purchase #6 $207.44   8.624%   $225.3296   $225.33   $225.35   $225.30  
  Purchase #7 $65.35   4.159%   $68.0679   $68.07   $68.05   $68.10  
  7 purchase totals = $873.69       $943.1744   $943.18   $943.20   $943.20