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 $114.85   6.186%   $121.9546   $121.95   $121.95   $122.00  
  Purchase #2 $215.38   4.790%   $225.6967   $225.70   $225.70   $225.70  
  Purchase #3 $28.47   9.402%   $31.1467   $31.15   $31.15   $31.10  
  Purchase #4 $171.77   10.206%   $189.3008   $189.30   $189.30   $189.30  
  Purchase #5 $246.62   3.691%   $255.7227   $255.72   $255.70   $255.70  
  Purchase #6 $57.69   6.513%   $61.4473   $61.45   $61.45   $61.40  
  Purchase #7 $98.34   11.498%   $109.6471   $109.65   $109.65   $109.60  
  7 purchase totals = $933.12       $994.9159   $994.92   $994.90   $994.80