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 $235.50   9.809%   $258.6002   $258.60   $258.60   $258.60  
  Purchase #2 $20.69   5.646%   $21.8582   $21.86   $21.85   $21.90  
  Purchase #3 $13.60   8.833%   $14.8013   $14.80   $14.80   $14.80  
  Purchase #4 $68.86   9.730%   $75.5601   $75.56   $75.55   $75.60  
  Purchase #5 $203.84   13.861%   $232.0943   $232.09   $232.10   $232.10  
  Purchase #6 $94.49   11.290%   $105.1579   $105.16   $105.15   $105.20  
  Purchase #7 $224.26   5.469%   $236.5248   $236.52   $236.50   $236.50  
  7 purchase totals = $861.24       $944.5968   $944.59   $944.55   $944.70