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	$226.91	9.616%	$248.7297	$248.73	$248.75	$248.70
Purchase #2	$99.69	4.138%	$103.8152	$103.82	$103.80	$103.80
Purchase #3	$172.84	13.692%	$196.5053	$196.51	$196.50	$196.50
Purchase #4	$233.65	12.700%	$263.3236	$263.32	$263.30	$263.30
Purchase #5	$187.36	4.866%	$196.4769	$196.48	$196.50	$196.50
Purchase #6	$184.40	10.796%	$204.3078	$204.31	$204.30	$204.30
Purchase #7	$213.32	13.874%	$242.916	$242.92	$242.90	$242.90
7 purchase totals =	$1,318.17		$1,456.0745	$1,456.09	$1,456.05	$1,456.00