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 $61.90   11.227%   $68.8495   $68.85   $68.85   $68.80  
  Purchase #2 $163.49   5.432%   $172.3708   $172.37   $172.35   $172.40  
  Purchase #3 $92.43   9.240%   $100.9705   $100.97   $100.95   $101.00  
  Purchase #4 $240.68   4.232%   $250.8656   $250.87   $250.85   $250.90  
  Purchase #5 $167.74   11.491%   $187.015   $187.02   $187.00   $187.00  
  Purchase #6 $132.60   7.258%   $142.2241   $142.22   $142.20   $142.20  
  Purchase #7 $89.34   9.357%   $97.6995   $97.70   $97.70   $97.70  
  7 purchase totals = $948.18       $1,019.9950   $1,020.00   $1,019.90   $1,020.00