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 $70.65   5.465%   $74.511   $74.51   $74.50   $74.50  
  Purchase #2 $193.56   5.730%   $204.651   $204.65   $204.65   $204.70  
  Purchase #3 $70.27   6.235%   $74.6513   $74.65   $74.65   $74.70  
  Purchase #4 $124.28   10.873%   $137.793   $137.79   $137.80   $137.80  
  Purchase #5 $163.99   7.259%   $175.894   $175.89   $175.90   $175.90  
  Purchase #6 $79.86   12.245%   $89.6389   $89.64   $89.65   $89.60  
  Purchase #7 $61.55   3.312%   $63.5885   $63.59   $63.60   $63.60  
  7 purchase totals = $764.16       $820.7277   $820.72   $820.75   $820.80