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 $86.79   6.298%   $92.256   $92.26   $92.25   $92.30  
  Purchase #2 $85.62   12.513%   $96.3336   $96.33   $96.35   $96.30  
  Purchase #3 $55.62   3.602%   $57.6234   $57.62   $57.60   $57.60  
  Purchase #4 $46.61   5.617%   $49.2281   $49.23   $49.25   $49.20  
  Purchase #5 $39.91   11.491%   $44.4961   $44.50   $44.50   $44.50  
  Purchase #6 $32.82   5.507%   $34.6274   $34.63   $34.65   $34.60  
  Purchase #7 $47.79   9.592%   $52.374   $52.37   $52.35   $52.40  
  7 purchase totals = $395.16       $426.9386   $426.94   $426.95   $426.90