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	$49.60	7.267%	$53.2044	$53.20	$53.20	$53.20
Purchase #2	$40.91	10.764%	$45.3136	$45.31	$45.30	$45.30
Purchase #3	$118.96	10.281%	$131.1903	$131.19	$131.20	$131.20
Purchase #4	$36.82	11.672%	$41.1176	$41.12	$41.10	$41.10
Purchase #5	$82.53	4.434%	$86.1894	$86.19	$86.20	$86.20
Purchase #6	$52.33	10.281%	$57.71	$57.71	$57.70	$57.70
Purchase #7	$171.94	13.264%	$194.7461	$194.75	$194.75	$194.70
7 purchase totals =	$553.09		$609.4714	$609.47	$609.45	$609.40