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 $54.83   6.718%   $58.5135   $58.51   $58.50   $58.50  
  Purchase #2 $192.68   5.126%   $202.5568   $202.56   $202.55   $202.60  
  Purchase #3 $141.86   7.531%   $152.5435   $152.54   $152.55   $152.50  
  Purchase #4 $130.74   3.324%   $135.0858   $135.09   $135.10   $135.10  
  Purchase #5 $217.95   7.318%   $233.8996   $233.90   $233.90   $233.90  
  Purchase #6 $22.54   5.781%   $23.843   $23.84   $23.85   $23.80  
  Purchase #7 $110.90   4.202%   $115.56   $115.56   $115.55   $115.60  
  7 purchase totals = $871.50       $922.0022   $922.00   $922.00   $922.00