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 $112.76   10.268%   $124.3382   $124.34   $124.35   $124.30  
  Purchase #2 $94.91   8.496%   $102.9736   $102.97   $102.95   $103.00  
  Purchase #3 $106.56   11.463%   $118.775   $118.78   $118.80   $118.80  
  Purchase #4 $151.82   3.860%   $157.6803   $157.68   $157.70   $157.70  
  Purchase #5 $44.94   4.268%   $46.858   $46.86   $46.85   $46.90  
  Purchase #6 $198.75   3.560%   $205.8255   $205.83   $205.85   $205.80  
  Purchase #7 $148.93   10.185%   $164.0985   $164.10   $164.10   $164.10  
  7 purchase totals = $858.67       $920.5491   $920.56   $920.60   $920.60