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 $176.33   5.851%   $186.6471   $186.65   $186.65   $186.60  
  Purchase #2 $177.31   8.688%   $192.7147   $192.71   $192.70   $192.70  
  Purchase #3 $156.34   5.473%   $164.8965   $164.90   $164.90   $164.90  
  Purchase #4 $247.48   11.486%   $275.9056   $275.91   $275.90   $275.90  
  Purchase #5 $76.56   6.241%   $81.3381   $81.34   $81.35   $81.30  
  Purchase #6 $161.74   9.501%   $177.1069   $177.11   $177.10   $177.10  
  Purchase #7 $85.32   10.207%   $94.0286   $94.03   $94.05   $94.00  
  7 purchase totals = $1,081.08       $1,172.6375   $1,172.65   $1,172.65   $1,172.50