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 $29.39   9.111%   $32.0677   $32.07   $32.05   $32.10  
  Purchase #2 $236.65   5.219%   $249.0008   $249.00   $249.00   $249.00  
  Purchase #3 $155.48   8.657%   $168.9399   $168.94   $168.95   $168.90  
  Purchase #4 $139.68   8.402%   $151.4159   $151.42   $151.40   $151.40  
  Purchase #5 $8.70   7.714%   $9.3711   $9.37   $9.35   $9.40  
  Purchase #6 $191.43   5.192%   $201.369   $201.37   $201.35   $201.40  
  Purchase #7 $233.59   3.439%   $241.6232   $241.62   $241.60   $241.60  
  7 purchase totals = $994.92       $1,053.7876   $1,053.79   $1,053.70   $1,053.80