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 $66.72   3.730%   $69.2087   $69.21   $69.20   $69.20  
  Purchase #2 $168.34   9.701%   $184.6707   $184.67   $184.65   $184.70  
  Purchase #3 $72.72   12.349%   $81.7002   $81.70   $81.70   $81.70  
  Purchase #4 $42.50   3.833%   $44.129   $44.13   $44.15   $44.10  
  Purchase #5 $141.92   6.382%   $150.9773   $150.98   $151.00   $151.00  
  Purchase #6 $249.48   8.187%   $269.9049   $269.90   $269.90   $269.90  
  Purchase #7 $152.65   7.679%   $164.372   $164.37   $164.35   $164.40  
  7 purchase totals = $894.33       $964.9628   $964.96   $964.95   $965.00