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 $225.51   11.705%   $251.9059   $251.91   $251.90   $251.90  
  Purchase #2 $104.30   7.355%   $111.9713   $111.97   $111.95   $112.00  
  Purchase #3 $209.98   5.395%   $221.3084   $221.31   $221.30   $221.30  
  Purchase #4 $70.56   9.520%   $77.2773   $77.28   $77.30   $77.30  
  Purchase #5 $102.92   4.453%   $107.503   $107.50   $107.50   $107.50  
  Purchase #6 $230.73   12.374%   $259.2805   $259.28   $259.30   $259.30  
  Purchase #7 $27.85   12.201%   $31.248   $31.25   $31.25   $31.20  
  7 purchase totals = $971.85       $1,060.4944   $1,060.50   $1,060.50   $1,060.50