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 $23.58   13.328%   $26.7227   $26.72   $26.70   $26.70  
  Purchase #2 $88.50   8.761%   $96.2535   $96.25   $96.25   $96.30  
  Purchase #3 $86.85   13.217%   $98.329   $98.33   $98.35   $98.30  
  Purchase #4 $34.68   10.578%   $38.3485   $38.35   $38.35   $38.30  
  Purchase #5 $220.55   11.770%   $246.5087   $246.51   $246.50   $246.50  
  Purchase #6 $84.50   3.856%   $87.7583   $87.76   $87.75   $87.80  
  Purchase #7 $163.94   4.774%   $171.7665   $171.77   $171.75   $171.80  
  7 purchase totals = $702.60       $765.6872   $765.69   $765.65   $765.70