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 $119.94   5.456%   $126.4839   $126.48   $126.50   $126.50  
  Purchase #2 $41.57   9.669%   $45.5894   $45.59   $45.60   $45.60  
  Purchase #3 $64.67   7.707%   $69.6541   $69.65   $69.65   $69.70  
  Purchase #4 $183.97   10.713%   $203.6787   $203.68   $203.70   $203.70  
  Purchase #5 $44.59   3.869%   $46.3152   $46.32   $46.30   $46.30  
  Purchase #6 $34.30   7.481%   $36.866   $36.87   $36.85   $36.90  
  Purchase #7 $184.93   13.144%   $209.2372   $209.24   $209.25   $209.20  
  7 purchase totals = $673.97       $737.8245   $737.83   $737.85   $737.90