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 $119.46   8.514%   $129.6308   $129.63   $129.65   $129.60  
  Purchase #2 $19.56   11.388%   $21.7875   $21.79   $21.80   $21.80  
  Purchase #3 $136.63   8.157%   $147.7749   $147.77   $147.75   $147.80  
  Purchase #4 $37.41   10.191%   $41.2225   $41.22   $41.20   $41.20  
  Purchase #5 $186.32   7.779%   $200.8138   $200.81   $200.80   $200.80  
  Purchase #6 $134.31   12.829%   $151.5406   $151.54   $151.55   $151.50  
  Purchase #7 $59.92   3.848%   $62.2257   $62.23   $62.25   $62.20  
  7 purchase totals = $693.61       $754.9958   $754.99   $755.00   $754.90