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 $126.68   3.465%   $131.0695   $131.07   $131.05   $131.10  
  Purchase #2 $102.80   11.373%   $114.4914   $114.49   $114.50   $114.50  
  Purchase #3 $114.44   3.804%   $118.7933   $118.79   $118.80   $118.80  
  Purchase #4 $249.96   4.855%   $262.0956   $262.10   $262.10   $262.10  
  Purchase #5 $57.48   9.372%   $62.867   $62.87   $62.85   $62.90  
  Purchase #6 $178.39   12.295%   $200.3231   $200.32   $200.30   $200.30  
  Purchase #7 $12.87   8.604%   $13.9773   $13.98   $14.00   $14.00  
  7 purchase totals = $842.62       $903.6172   $903.62   $903.60   $903.70