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 $41.46   6.132%   $44.0023   $44.00   $44.00   $44.00  
  Purchase #2 $166.99   12.464%   $187.8036   $187.80   $187.80   $187.80  
  Purchase #3 $10.47   8.287%   $11.3376   $11.34   $11.35   $11.30  
  Purchase #4 $69.33   9.285%   $75.7673   $75.77   $75.75   $75.80  
  Purchase #5 $234.69   4.776%   $245.8988   $245.90   $245.90   $245.90  
  Purchase #6 $96.35   13.835%   $109.68   $109.68   $109.70   $109.70  
  Purchase #7 $67.67   3.445%   $70.0012   $70.00   $70.00   $70.00  
  7 purchase totals = $686.96       $744.4908   $744.49   $744.50   $744.50