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 $220.38   9.366%   $241.0208   $241.02   $241.00   $241.00  
  Purchase #2 $225.61   10.513%   $249.3284   $249.33   $249.35   $249.30  
  Purchase #3 $196.60   10.109%   $216.4743   $216.47   $216.45   $216.50  
  Purchase #4 $53.75   12.388%   $60.4086   $60.41   $60.40   $60.40  
  Purchase #5 $124.32   13.446%   $141.0361   $141.04   $141.05   $141.00  
  Purchase #6 $204.72   3.142%   $211.1523   $211.15   $211.15   $211.20  
  Purchase #7 $134.57   9.611%   $147.5035   $147.50   $147.50   $147.50  
  7 purchase totals = $1,159.95       $1,266.9240   $1,266.92   $1,266.90   $1,266.90