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 $67.36   9.623%   $73.8421   $73.84   $73.85   $73.80  
  Purchase #2 $12.65   5.480%   $13.3432   $13.34   $13.35   $13.30  
  Purchase #3 $233.60   6.144%   $247.9524   $247.95   $247.95   $248.00  
  Purchase #4 $173.76   9.104%   $189.5791   $189.58   $189.60   $189.60  
  Purchase #5 $8.30   5.124%   $8.7253   $8.73   $8.75   $8.70  
  Purchase #6 $194.47   10.541%   $214.9691   $214.97   $214.95   $215.00  
  Purchase #7 $192.97   5.823%   $204.2066   $204.21   $204.20   $204.20  
  7 purchase totals = $883.11       $952.6178   $952.62   $952.65   $952.60