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 $65.26   8.794%   $70.999   $71.00   $71.00   $71.00  
  Purchase #2 $233.71   7.144%   $250.4062   $250.41   $250.40   $250.40  
  Purchase #3 $44.34   8.113%   $47.9373   $47.94   $47.95   $47.90  
  Purchase #4 $70.78   13.418%   $80.2773   $80.28   $80.30   $80.30  
  Purchase #5 $202.70   6.400%   $215.6728   $215.67   $215.65   $215.70  
  Purchase #6 $11.67   5.477%   $12.3092   $12.31   $12.30   $12.30  
  Purchase #7 $242.77   3.233%   $250.6188   $250.62   $250.60   $250.60  
  7 purchase totals = $871.23       $928.2206   $928.23   $928.20   $928.20