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 $235.65   11.407%   $262.5306   $262.53   $262.55   $262.50  
  Purchase #2 $225.46   13.308%   $255.4642   $255.46   $255.45   $255.50  
  Purchase #3 $144.35   9.671%   $158.3101   $158.31   $158.30   $158.30  
  Purchase #4 $228.84   5.427%   $241.2591   $241.26   $241.25   $241.30  
  Purchase #5 $225.40   3.835%   $234.0441   $234.04   $234.05   $234.00  
  Purchase #6 $225.50   5.283%   $237.4132   $237.41   $237.40   $237.40  
  Purchase #7 $48.28   11.361%   $53.7651   $53.77   $53.75   $53.80  
  7 purchase totals = $1,333.48       $1,442.7864   $1,442.78   $1,442.75   $1,442.80