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 $236.78   4.109%   $246.5093   $246.51   $246.50   $246.50  
  Purchase #2 $11.48   3.121%   $11.8383   $11.84   $11.85   $11.80  
  Purchase #3 $130.72   6.800%   $139.609   $139.61   $139.60   $139.60  
  Purchase #4 $247.35   12.162%   $277.4327   $277.43   $277.45   $277.40  
  Purchase #5 $73.94   6.637%   $78.8474   $78.85   $78.85   $78.80  
  Purchase #6 $128.94   8.553%   $139.9682   $139.97   $139.95   $140.00  
  Purchase #7 $176.49   3.688%   $182.999   $183.00   $183.00   $183.00  
  7 purchase totals = $1,005.70       $1,077.2039   $1,077.21   $1,077.20   $1,077.10