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 $131.41   12.139%   $147.3619   $147.36   $147.35   $147.40  
  Purchase #2 $220.54   8.243%   $238.7191   $238.72   $238.70   $238.70  
  Purchase #3 $221.99   3.359%   $229.4466   $229.45   $229.45   $229.40  
  Purchase #4 $184.92   5.816%   $195.6749   $195.67   $195.65   $195.70  
  Purchase #5 $155.70   8.133%   $168.3631   $168.36   $168.35   $168.40  
  Purchase #6 $117.86   7.105%   $126.234   $126.23   $126.25   $126.20  
  Purchase #7 $91.91   6.433%   $97.8226   $97.82   $97.80   $97.80  
  7 purchase totals = $1,124.33       $1,203.6222   $1,203.61   $1,203.55   $1,203.60