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 $48.64   7.364%   $52.2218   $52.22   $52.20   $52.20  
  Purchase #2 $226.90   13.632%   $257.831   $257.83   $257.85   $257.80  
  Purchase #3 $91.73   6.223%   $97.4384   $97.44   $97.45   $97.40  
  Purchase #4 $225.35   4.477%   $235.4389   $235.44   $235.45   $235.40  
  Purchase #5 $30.48   13.763%   $34.675   $34.68   $34.70   $34.70  
  Purchase #6 $249.97   11.474%   $278.6516   $278.65   $278.65   $278.70  
  Purchase #7 $226.75   6.591%   $241.6951   $241.70   $241.70   $241.70  
  7 purchase totals = $1,099.82       $1,197.9518   $1,197.96   $1,198.00   $1,197.90