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 $47.98   13.643%   $54.5259   $54.53   $54.55   $54.50  
  Purchase #2 $96.82   10.750%   $107.2282   $107.23   $107.25   $107.20  
  Purchase #3 $147.64   8.812%   $160.65   $160.65   $160.65   $160.70  
  Purchase #4 $51.36   6.658%   $54.7795   $54.78   $54.80   $54.80  
  Purchase #5 $213.59   11.207%   $237.527   $237.53   $237.55   $237.50  
  Purchase #6 $243.99   13.428%   $276.753   $276.75   $276.75   $276.80  
  Purchase #7 $44.90   12.412%   $50.473   $50.47   $50.45   $50.50  
  7 purchase totals = $846.28       $941.9366   $941.94   $942.00   $942.00