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 $225.29   13.486%   $255.6726   $255.67   $255.65   $255.70  
  Purchase #2 $45.78   7.105%   $49.0327   $49.03   $49.05   $49.00  
  Purchase #3 $207.89   6.793%   $222.012   $222.01   $222.00   $222.00  
  Purchase #4 $180.28   4.817%   $188.9641   $188.96   $188.95   $189.00  
  Purchase #5 $52.40   7.245%   $56.1964   $56.20   $56.20   $56.20  
  Purchase #6 $44.31   5.525%   $46.7581   $46.76   $46.75   $46.80  
  Purchase #7 $213.68   13.176%   $241.8345   $241.83   $241.85   $241.80  
  7 purchase totals = $969.63       $1,060.4704   $1,060.46   $1,060.45   $1,060.50