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 $51.86   8.639%   $56.3402   $56.34   $56.35   $56.30  
  Purchase #2 $98.41   11.619%   $109.8443   $109.84   $109.85   $109.80  
  Purchase #3 $149.83   12.730%   $168.9034   $168.90   $168.90   $168.90  
  Purchase #4 $220.43   7.635%   $237.2598   $237.26   $237.25   $237.30  
  Purchase #5 $147.75   10.120%   $162.7023   $162.70   $162.70   $162.70  
  Purchase #6 $214.48   7.251%   $230.0319   $230.03   $230.05   $230.00  
  Purchase #7 $48.46   3.872%   $50.3364   $50.34   $50.35   $50.30  
  7 purchase totals = $931.22       $1,015.4183   $1,015.41   $1,015.45   $1,015.30