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 $73.33   3.284%   $75.7382   $75.74   $75.75   $75.70  
  Purchase #2 $244.71   8.759%   $266.1441   $266.14   $266.15   $266.10  
  Purchase #3 $62.72   6.528%   $66.8144   $66.81   $66.80   $66.80  
  Purchase #4 $233.92   5.196%   $246.0745   $246.07   $246.05   $246.10  
  Purchase #5 $6.60   9.674%   $7.2385   $7.24   $7.25   $7.20  
  Purchase #6 $91.45   4.604%   $95.6604   $95.66   $95.65   $95.70  
  Purchase #7 $136.74   10.689%   $151.3561   $151.36   $151.35   $151.40  
  7 purchase totals = $849.47       $909.0262   $909.02   $909.00   $909.00