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 $30.26   8.311%   $32.7749   $32.77   $32.75   $32.80  
  Purchase #2 $235.63   8.214%   $254.9846   $254.98   $255.00   $255.00  
  Purchase #3 $151.92   11.208%   $168.9472   $168.95   $168.95   $168.90  
  Purchase #4 $211.82   8.669%   $230.1827   $230.18   $230.20   $230.20  
  Purchase #5 $179.49   4.247%   $187.1129   $187.11   $187.10   $187.10  
  Purchase #6 $113.64   5.594%   $119.997   $120.00   $120.00   $120.00  
  Purchase #7 $209.81   4.807%   $219.8956   $219.90   $219.90   $219.90  
  7 purchase totals = $1,132.57       $1,213.8949   $1,213.89   $1,213.90   $1,213.90