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 $116.44   4.427%   $121.5948   $121.59   $121.60   $121.60  
  Purchase #2 $207.47   9.874%   $227.9556   $227.96   $227.95   $228.00  
  Purchase #3 $81.55   12.180%   $91.4828   $91.48   $91.50   $91.50  
  Purchase #4 $203.99   8.315%   $220.9518   $220.95   $220.95   $221.00  
  Purchase #5 $245.75   12.188%   $275.702   $275.70   $275.70   $275.70  
  Purchase #6 $242.35   5.592%   $255.9022   $255.90   $255.90   $255.90  
  Purchase #7 $49.61   12.656%   $55.8886   $55.89   $55.90   $55.90  
  7 purchase totals = $1,147.16       $1,249.4778   $1,249.47   $1,249.50   $1,249.60