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 $213.53   11.363%   $237.7934   $237.79   $237.80   $237.80  
  Purchase #2 $35.53   10.522%   $39.2685   $39.27   $39.25   $39.30  
  Purchase #3 $101.37   8.819%   $110.3098   $110.31   $110.30   $110.30  
  Purchase #4 $245.51   11.219%   $273.0538   $273.05   $273.05   $273.10  
  Purchase #5 $250.75   12.542%   $282.1991   $282.20   $282.20   $282.20  
  Purchase #6 $9.90   4.824%   $10.3776   $10.38   $10.40   $10.40  
  Purchase #7 $198.66   7.729%   $214.0144   $214.01   $214.00   $214.00  
  7 purchase totals = $1,055.25       $1,167.0166   $1,167.01   $1,167.00   $1,167.10