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	$133.33	4.531%	$139.3712	$139.37	$139.35	$139.40
Purchase #2	$198.38	10.554%	$219.317	$219.32	$219.30	$219.30
Purchase #3	$209.69	10.826%	$232.391	$232.39	$232.40	$232.40
Purchase #4	$82.62	11.673%	$92.2642	$92.26	$92.25	$92.30
Purchase #5	$183.44	7.174%	$196.6	$196.60	$196.60	$196.60
Purchase #6	$202.88	7.475%	$218.0453	$218.05	$218.05	$218.00
Purchase #7	$168.96	12.640%	$190.3165	$190.32	$190.30	$190.30
7 purchase totals =	$1,179.30		$1,288.3052	$1,288.31	$1,288.25	$1,288.30