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 $225.87   9.359%   $247.0092   $247.01   $247.00   $247.00  
  Purchase #2 $188.47   7.661%   $202.9087   $202.91   $202.90   $202.90  
  Purchase #3 $11.62   6.667%   $12.3947   $12.39   $12.40   $12.40  
  Purchase #4 $30.30   6.222%   $32.1853   $32.19   $32.20   $32.20  
  Purchase #5 $106.53   8.673%   $115.7693   $115.77   $115.75   $115.80  
  Purchase #6 $160.86   13.223%   $182.1305   $182.13   $182.15   $182.10  
  Purchase #7 $222.82   4.158%   $232.0849   $232.08   $232.10   $232.10  
  7 purchase totals = $946.47       $1,024.4826   $1,024.48   $1,024.50   $1,024.50