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 $205.61   9.286%   $224.7029   $224.70   $224.70   $224.70  
  Purchase #2 $69.57   11.298%   $77.43   $77.43   $77.45   $77.40  
  Purchase #3 $137.71   12.226%   $154.5464   $154.55   $154.55   $154.50  
  Purchase #4 $48.87   8.125%   $52.8407   $52.84   $52.85   $52.80  
  Purchase #5 $76.68   7.559%   $82.4762   $82.48   $82.50   $82.50  
  Purchase #6 $60.81   8.862%   $66.199   $66.20   $66.20   $66.20  
  Purchase #7 $149.93   7.169%   $160.6785   $160.68   $160.70   $160.70  
  7 purchase totals = $749.18       $818.8737   $818.88   $818.95   $818.80