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 $62.74   6.782%   $66.995   $67.00   $67.00   $67.00  
  Purchase #2 $88.81   13.498%   $100.7976   $100.80   $100.80   $100.80  
  Purchase #3 $88.67   6.381%   $94.328   $94.33   $94.35   $94.30  
  Purchase #4 $126.59   8.406%   $137.2312   $137.23   $137.25   $137.20  
  Purchase #5 $39.39   13.341%   $44.645   $44.65   $44.65   $44.60  
  Purchase #6 $27.77   3.236%   $28.6686   $28.67   $28.65   $28.70  
  Purchase #7 $15.93   4.209%   $16.6005   $16.60   $16.60   $16.60  
  7 purchase totals = $449.90       $489.2659   $489.28   $489.30   $489.20