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 $61.35   5.352%   $64.6335   $64.63   $64.65   $64.60  
  Purchase #2 $194.43   3.655%   $201.5364   $201.54   $201.55   $201.50  
  Purchase #3 $74.58   9.208%   $81.4473   $81.45   $81.45   $81.40  
  Purchase #4 $238.75   13.120%   $270.074   $270.07   $270.05   $270.10  
  Purchase #5 $183.85   13.379%   $208.4473   $208.45   $208.45   $208.40  
  Purchase #6 $157.32   11.555%   $175.4983   $175.50   $175.50   $175.50  
  Purchase #7 $249.58   10.446%   $275.6511   $275.65   $275.65   $275.70  
  7 purchase totals = $1,159.86       $1,277.2879   $1,277.29   $1,277.30   $1,277.20