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 $246.37   12.616%   $277.452   $277.45   $277.45   $277.50  
  Purchase #2 $237.39   13.582%   $269.6323   $269.63   $269.65   $269.60  
  Purchase #3 $201.83   13.594%   $229.2668   $229.27   $229.25   $229.30  
  Purchase #4 $249.92   9.422%   $273.4675   $273.47   $273.45   $273.50  
  Purchase #5 $246.32   6.505%   $262.3431   $262.34   $262.35   $262.30  
  Purchase #6 $125.79   4.648%   $131.6367   $131.64   $131.65   $131.60  
  Purchase #7 $111.54   9.201%   $121.8028   $121.80   $121.80   $121.80  
  7 purchase totals = $1,419.16       $1,565.6012   $1,565.60   $1,565.60   $1,565.60