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	$197.63	12.490%	$222.314	$222.31	$222.30	$222.30
Purchase #2	$124.78	11.499%	$139.1285	$139.13	$139.15	$139.10
Purchase #3	$116.39	11.782%	$130.1031	$130.10	$130.10	$130.10
Purchase #4	$210.95	13.465%	$239.3544	$239.35	$239.35	$239.40
Purchase #5	$169.67	9.391%	$185.6037	$185.60	$185.60	$185.60
Purchase #6	$31.47	7.668%	$33.8831	$33.88	$33.90	$33.90
Purchase #7	$42.44	3.591%	$43.964	$43.96	$43.95	$44.00
7 purchase totals =	$893.33		$994.3508	$994.33	$994.35	$994.40