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 $204.82   11.291%   $227.9462   $227.95   $227.95   $227.90  
  Purchase #2 $214.97   10.237%   $236.9765   $236.98   $237.00   $237.00  
  Purchase #3 $79.78   4.363%   $83.2608   $83.26   $83.25   $83.30  
  Purchase #4 $58.31   4.198%   $60.7579   $60.76   $60.75   $60.80  
  Purchase #5 $38.44   5.749%   $40.6499   $40.65   $40.65   $40.60  
  Purchase #6 $59.31   13.502%   $67.318   $67.32   $67.30   $67.30  
  Purchase #7 $71.59   12.549%   $80.5738   $80.57   $80.55   $80.60  
  7 purchase totals = $727.22       $797.4831   $797.49   $797.45   $797.50