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 $183.76   12.790%   $207.2629   $207.26   $207.25   $207.30  
  Purchase #2 $83.95   10.430%   $92.706   $92.71   $92.70   $92.70  
  Purchase #3 $101.44   4.421%   $105.9247   $105.92   $105.90   $105.90  
  Purchase #4 $93.34   6.333%   $99.2512   $99.25   $99.25   $99.30  
  Purchase #5 $201.96   13.362%   $228.9459   $228.95   $228.95   $228.90  
  Purchase #6 $231.43   5.281%   $243.6518   $243.65   $243.65   $243.70  
  Purchase #7 $71.27   6.620%   $75.9881   $75.99   $76.00   $76.00  
  7 purchase totals = $967.15       $1,053.7306   $1,053.73   $1,053.70   $1,053.80