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 $66.82   13.180%   $75.6269   $75.63   $75.65   $75.60  
  Purchase #2 $166.42   10.695%   $184.2186   $184.22   $184.20   $184.20  
  Purchase #3 $21.41   3.460%   $22.1508   $22.15   $22.15   $22.20  
  Purchase #4 $117.99   5.470%   $124.4441   $124.44   $124.45   $124.40  
  Purchase #5 $87.36   10.679%   $96.6892   $96.69   $96.70   $96.70  
  Purchase #6 $198.65   13.663%   $225.7915   $225.79   $225.80   $225.80  
  Purchase #7 $208.71   9.806%   $229.1761   $229.18   $229.20   $229.20  
  7 purchase totals = $867.36       $958.0972   $958.10   $958.15   $958.10