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 $83.34   12.225%   $93.5283   $93.53   $93.55   $93.50  
  Purchase #2 $155.71   13.196%   $176.2575   $176.26   $176.25   $176.30  
  Purchase #3 $62.84   5.351%   $66.2026   $66.20   $66.20   $66.20  
  Purchase #4 $69.98   5.255%   $73.6574   $73.66   $73.65   $73.70  
  Purchase #5 $190.52   13.392%   $216.0344   $216.03   $216.05   $216.00  
  Purchase #6 $144.45   10.115%   $159.0611   $159.06   $159.05   $159.10  
  Purchase #7 $146.39   9.792%   $160.7245   $160.72   $160.70   $160.70  
  7 purchase totals = $853.23       $945.4658   $945.46   $945.45   $945.50