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	$109.49	7.350%	$117.5375	$117.54	$117.55	$117.50
Purchase #2	$125.86	12.284%	$141.3206	$141.32	$141.30	$141.30
Purchase #3	$71.47	13.229%	$80.9248	$80.92	$80.90	$80.90
Purchase #4	$154.49	11.815%	$172.743	$172.74	$172.75	$172.70
Purchase #5	$154.80	5.201%	$162.8511	$162.85	$162.85	$162.90
Purchase #6	$86.31	11.758%	$96.4583	$96.46	$96.45	$96.50
Purchase #7	$135.82	11.384%	$151.2817	$151.28	$151.30	$151.30
7 purchase totals =	$838.24		$923.1170	$923.11	$923.10	$923.10