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 $215.73   3.553%   $223.3949   $223.39   $223.40   $223.40  
  Purchase #2 $119.76   3.511%   $123.9648   $123.96   $123.95   $124.00  
  Purchase #3 $105.52   13.415%   $119.6755   $119.68   $119.70   $119.70  
  Purchase #4 $94.88   13.265%   $107.4658   $107.47   $107.45   $107.50  
  Purchase #5 $213.44   3.687%   $221.3095   $221.31   $221.30   $221.30  
  Purchase #6 $45.90   9.716%   $50.3596   $50.36   $50.35   $50.40  
  Purchase #7 $162.37   9.731%   $178.1702   $178.17   $178.15   $178.20  
  7 purchase totals = $957.60       $1,024.3403   $1,024.34   $1,024.30   $1,024.50