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	$52.56	3.607%	$54.4558	$54.46	$54.45	$54.50
Purchase #2	$202.67	9.773%	$222.4769	$222.48	$222.50	$222.50
Purchase #3	$148.28	4.786%	$155.3767	$155.38	$155.40	$155.40
Purchase #4	$91.80	8.814%	$99.8913	$99.89	$99.90	$99.90
Purchase #5	$114.80	6.135%	$121.843	$121.84	$121.85	$121.80
Purchase #6	$154.56	13.380%	$175.2401	$175.24	$175.25	$175.20
Purchase #7	$150.94	7.677%	$162.5277	$162.53	$162.55	$162.50
7 purchase totals =	$915.61		$991.8115	$991.82	$991.90	$991.80