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 $129.60   5.590%   $136.8446   $136.84   $136.85   $136.80  
  Purchase #2 $48.74   3.802%   $50.5931   $50.59   $50.60   $50.60  
  Purchase #3 $208.50   9.116%   $227.5069   $227.51   $227.50   $227.50  
  Purchase #4 $210.84   12.508%   $237.2119   $237.21   $237.20   $237.20  
  Purchase #5 $161.56   5.197%   $169.9563   $169.96   $169.95   $170.00  
  Purchase #6 $145.62   4.694%   $152.4554   $152.46   $152.45   $152.50  
  Purchase #7 $228.78   13.395%   $259.4251   $259.43   $259.45   $259.40  
  7 purchase totals = $1,133.64       $1,233.9933   $1,234.00   $1,234.00   $1,234.00