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 $217.85   11.671%   $243.2753   $243.28   $243.30   $243.30  
  Purchase #2 $204.99   7.526%   $220.4175   $220.42   $220.40   $220.40  
  Purchase #3 $212.32   8.210%   $229.7515   $229.75   $229.75   $229.80  
  Purchase #4 $52.79   9.785%   $57.9555   $57.96   $57.95   $58.00  
  Purchase #5 $70.36   12.577%   $79.2092   $79.21   $79.20   $79.20  
  Purchase #6 $76.91   7.310%   $82.5321   $82.53   $82.55   $82.50  
  Purchase #7 $41.60   12.524%   $46.81   $46.81   $46.80   $46.80  
  7 purchase totals = $876.82       $959.9511   $959.96   $959.95   $960.00