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	$102.70	6.151%	$109.0171	$109.02	$109.00	$109.00
Purchase #2	$89.90	11.183%	$99.9535	$99.95	$99.95	$100.00
Purchase #3	$85.41	6.841%	$91.2529	$91.25	$91.25	$91.30
Purchase #4	$168.48	13.139%	$190.6166	$190.62	$190.60	$190.60
Purchase #5	$50.49	8.414%	$54.7382	$54.74	$54.75	$54.70
Purchase #6	$223.30	3.516%	$231.1512	$231.15	$231.15	$231.20
Purchase #7	$48.46	3.145%	$49.9841	$49.98	$50.00	$50.00
7 purchase totals =	$768.74		$826.7136	$826.71	$826.70	$826.80