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 $151.44   11.118%   $168.2771   $168.28   $168.30   $168.30  
  Purchase #2 $239.57   4.120%   $249.4403   $249.44   $249.45   $249.40  
  Purchase #3 $139.45   6.121%   $147.9857   $147.99   $148.00   $148.00  
  Purchase #4 $150.75   7.432%   $161.9537   $161.95   $161.95   $162.00  
  Purchase #5 $221.67   11.567%   $247.3106   $247.31   $247.30   $247.30  
  Purchase #6 $92.90   12.311%   $104.3369   $104.34   $104.35   $104.30  
  Purchase #7 $189.70   13.281%   $214.8941   $214.89   $214.90   $214.90  
  7 purchase totals = $1,185.48       $1,294.1984   $1,294.20   $1,294.25   $1,294.20