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 $111.40   13.117%   $126.0123   $126.01   $126.00   $126.00  
  Purchase #2 $74.44   13.373%   $84.3949   $84.39   $84.40   $84.40  
  Purchase #3 $81.41   6.154%   $86.42   $86.42   $86.40   $86.40  
  Purchase #4 $80.84   13.166%   $91.4834   $91.48   $91.50   $91.50  
  Purchase #5 $187.49   11.851%   $209.7094   $209.71   $209.70   $209.70  
  Purchase #6 $193.85   10.586%   $214.371   $214.37   $214.35   $214.40  
  Purchase #7 $57.64   13.238%   $65.2704   $65.27   $65.25   $65.30  
  7 purchase totals = $787.07       $877.6614   $877.65   $877.60   $877.70