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 $56.74   12.650%   $63.9176   $63.92   $63.90   $63.90  
  Purchase #2 $208.94   8.821%   $227.3706   $227.37   $227.35   $227.40  
  Purchase #3 $116.39   3.128%   $120.0307   $120.03   $120.05   $120.00  
  Purchase #4 $183.69   7.319%   $197.1343   $197.13   $197.15   $197.10  
  Purchase #5 $110.98   9.481%   $121.502   $121.50   $121.50   $121.50  
  Purchase #6 $214.98   10.185%   $236.8757   $236.88   $236.90   $236.90  
  Purchase #7 $228.27   6.330%   $242.7195   $242.72   $242.70   $242.70  
  7 purchase totals = $1,119.99       $1,209.5504   $1,209.55   $1,209.55   $1,209.50