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 $62.75   13.846%   $71.4384   $71.44   $71.45   $71.40  
  Purchase #2 $228.69   13.329%   $259.1721   $259.17   $259.15   $259.20  
  Purchase #3 $159.35   5.548%   $168.1907   $168.19   $168.20   $168.20  
  Purchase #4 $177.91   9.166%   $194.2172   $194.22   $194.20   $194.20  
  Purchase #5 $66.70   11.832%   $74.5919   $74.59   $74.60   $74.60  
  Purchase #6 $30.77   4.513%   $32.1587   $32.16   $32.15   $32.20  
  Purchase #7 $200.25   3.767%   $207.7934   $207.79   $207.80   $207.80  
  7 purchase totals = $926.42       $1,007.5624   $1,007.56   $1,007.55   $1,007.60