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 $152.63   6.119%   $161.9694   $161.97   $161.95   $162.00  
  Purchase #2 $77.77   7.161%   $83.3391   $83.34   $83.35   $83.30  
  Purchase #3 $5.40   10.335%   $5.9581   $5.96   $5.95   $6.00  
  Purchase #4 $177.66   9.592%   $194.7011   $194.70   $194.70   $194.70  
  Purchase #5 $104.92   4.536%   $109.6792   $109.68   $109.70   $109.70  
  Purchase #6 $87.73   9.837%   $96.36   $96.36   $96.35   $96.40  
  Purchase #7 $89.87   8.407%   $97.4254   $97.43   $97.45   $97.40  
  7 purchase totals = $695.98       $749.4323   $749.44   $749.45   $749.50