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	$197.89	13.860%	$225.3176	$225.32	$225.30	$225.30
Purchase #2	$74.68	7.746%	$80.4647	$80.46	$80.45	$80.50
Purchase #3	$218.56	11.152%	$242.9338	$242.93	$242.95	$242.90
Purchase #4	$226.41	6.386%	$240.8685	$240.87	$240.85	$240.90
Purchase #5	$82.59	8.150%	$89.3211	$89.32	$89.30	$89.30
Purchase #6	$79.48	3.316%	$82.1156	$82.12	$82.10	$82.10
Purchase #7	$233.78	11.600%	$260.8985	$260.90	$260.90	$260.90
7 purchase totals =	$1,113.39		$1,221.9198	$1,221.92	$1,221.85	$1,221.90