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   11.477%   $53.4867   $53.49   $53.50   $53.50  
  Purchase #2 $106.99   9.378%   $117.0235   $117.02   $117.00   $117.00  
  Purchase #3 $229.82   11.227%   $255.6219   $255.62   $255.60   $255.60  
  Purchase #4 $183.78   5.252%   $193.4321   $193.43   $193.45   $193.40  
  Purchase #5 $147.27   4.500%   $153.8972   $153.90   $153.90   $153.90  
  Purchase #6 $110.81   4.359%   $115.6402   $115.64   $115.65   $115.60  
  Purchase #7 $131.66   12.110%   $147.604   $147.60   $147.60   $147.60  
  7 purchase totals = $958.31       $1,036.7056   $1,036.70   $1,036.70   $1,036.60