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 $194.46   8.255%   $210.5127   $210.51   $210.50   $210.50  
  Purchase #2 $249.50   10.327%   $275.2659   $275.27   $275.25   $275.30  
  Purchase #3 $233.87   9.314%   $255.6527   $255.65   $255.65   $255.70  
  Purchase #4 $246.99   8.400%   $267.7372   $267.74   $267.75   $267.70  
  Purchase #5 $108.31   9.687%   $118.802   $118.80   $118.80   $118.80  
  Purchase #6 $200.63   5.869%   $212.405   $212.41   $212.40   $212.40  
  Purchase #7 $74.92   6.432%   $79.7389   $79.74   $79.75   $79.70  
  7 purchase totals = $1,308.68       $1,420.1144   $1,420.12   $1,420.10   $1,420.10