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 $54.31   5.605%   $57.3541   $57.35   $57.35   $57.40  
  Purchase #2 $202.34   5.686%   $213.8451   $213.85   $213.85   $213.80  
  Purchase #3 $112.42   6.410%   $119.6261   $119.63   $119.65   $119.60  
  Purchase #4 $130.68   7.763%   $140.8247   $140.82   $140.80   $140.80  
  Purchase #5 $80.73   9.570%   $88.4559   $88.46   $88.45   $88.50  
  Purchase #6 $209.26   4.183%   $218.0133   $218.01   $218.00   $218.00  
  Purchase #7 $186.94   4.652%   $195.6364   $195.64   $195.65   $195.60  
  7 purchase totals = $976.68       $1,033.7556   $1,033.76   $1,033.75   $1,033.70