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 $244.60   7.416%   $262.7395   $262.74   $262.75   $262.70  
  Purchase #2 $88.88   11.185%   $98.8212   $98.82   $98.80   $98.80  
  Purchase #3 $54.73   9.555%   $59.9595   $59.96   $59.95   $60.00  
  Purchase #4 $136.71   4.113%   $142.3329   $142.33   $142.35   $142.30  
  Purchase #5 $175.58   3.710%   $182.094   $182.09   $182.10   $182.10  
  Purchase #6 $190.44   12.612%   $214.4583   $214.46   $214.45   $214.50  
  Purchase #7 $162.34   9.275%   $177.397   $177.40   $177.40   $177.40  
  7 purchase totals = $1,053.28       $1,137.8024   $1,137.80   $1,137.80   $1,137.80