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 $19.29   8.471%   $20.9241   $20.92   $20.90   $20.90  
  Purchase #2 $28.54   8.609%   $30.997   $31.00   $31.00   $31.00  
  Purchase #3 $141.29   4.449%   $147.576   $147.58   $147.60   $147.60  
  Purchase #4 $144.67   5.118%   $152.0742   $152.07   $152.05   $152.10  
  Purchase #5 $19.51   5.697%   $20.6215   $20.62   $20.60   $20.60  
  Purchase #6 $198.67   11.263%   $221.0462   $221.05   $221.05   $221.00  
  Purchase #7 $133.45   11.471%   $148.758   $148.76   $148.75   $148.80  
  7 purchase totals = $685.42       $741.9970   $742.00   $741.95   $742.00