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 $217.59   13.868%   $247.7654   $247.77   $247.75   $247.80  
  Purchase #2 $76.83   6.489%   $81.8155   $81.82   $81.80   $81.80  
  Purchase #3 $155.56   5.116%   $163.5184   $163.52   $163.50   $163.50  
  Purchase #4 $204.66   8.134%   $221.307   $221.31   $221.30   $221.30  
  Purchase #5 $182.37   8.647%   $198.1395   $198.14   $198.15   $198.10  
  Purchase #6 $47.92   4.253%   $49.958   $49.96   $49.95   $50.00  
  Purchase #7 $244.67   7.523%   $263.0765   $263.08   $263.10   $263.10  
  7 purchase totals = $1,129.60       $1,225.5803   $1,225.60   $1,225.55   $1,225.60