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 $136.28   12.779%   $153.6952   $153.70   $153.70   $153.70  
  Purchase #2 $223.62   11.176%   $248.6118   $248.61   $248.60   $248.60  
  Purchase #3 $96.55   7.550%   $103.8395   $103.84   $103.85   $103.80  
  Purchase #4 $199.61   5.820%   $211.2273   $211.23   $211.25   $211.20  
  Purchase #5 $77.60   7.568%   $83.4728   $83.47   $83.45   $83.50  
  Purchase #6 $50.81   11.513%   $56.6598   $56.66   $56.65   $56.70  
  Purchase #7 $113.82   10.667%   $125.9612   $125.96   $125.95   $126.00  
  7 purchase totals = $898.29       $983.4676   $983.47   $983.45   $983.50