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 $238.59   8.216%   $258.1926   $258.19   $258.20   $258.20  
  Purchase #2 $223.99   11.357%   $249.4285   $249.43   $249.45   $249.40  
  Purchase #3 $61.59   7.181%   $66.0128   $66.01   $66.00   $66.00  
  Purchase #4 $96.65   6.510%   $102.9419   $102.94   $102.95   $102.90  
  Purchase #5 $42.76   5.538%   $45.128   $45.13   $45.15   $45.10  
  Purchase #6 $208.30   4.791%   $218.2797   $218.28   $218.30   $218.30  
  Purchase #7 $135.89   12.732%   $153.1915   $153.19   $153.20   $153.20  
  7 purchase totals = $1,007.77       $1,093.1750   $1,093.17   $1,093.25   $1,093.10