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	$93.98	6.309%	$99.9092	$99.91	$99.90	$99.90
Purchase #2	$185.48	13.201%	$209.9652	$209.97	$209.95	$210.00
Purchase #3	$103.52	6.589%	$110.3409	$110.34	$110.35	$110.30
Purchase #4	$238.92	8.336%	$258.8364	$258.84	$258.85	$258.80
Purchase #5	$72.27	13.778%	$82.2274	$82.23	$82.25	$82.20
Purchase #6	$106.85	4.412%	$111.5642	$111.56	$111.55	$111.60
Purchase #7	$197.72	9.352%	$216.2108	$216.21	$216.20	$216.20
7 purchase totals =	$998.74		$1,089.0541	$1,089.06	$1,089.05	$1,089.00