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 $208.45   8.190%   $225.5221   $225.52   $225.50   $225.50  
  Purchase #2 $12.95   10.872%   $14.3579   $14.36   $14.35   $14.40  
  Purchase #3 $229.77   6.177%   $243.9629   $243.96   $243.95   $244.00  
  Purchase #4 $23.48   4.487%   $24.5335   $24.53   $24.55   $24.50  
  Purchase #5 $188.98   5.359%   $199.1074   $199.11   $199.10   $199.10  
  Purchase #6 $229.52   4.253%   $239.2815   $239.28   $239.30   $239.30  
  Purchase #7 $33.99   5.492%   $35.8567   $35.86   $35.85   $35.90  
  7 purchase totals = $927.14       $982.6220   $982.62   $982.60   $982.70