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	$89.69	10.614%	$99.2097	$99.21	$99.20	$99.20
Purchase #2	$166.83	11.319%	$185.7135	$185.71	$185.70	$185.70
Purchase #3	$160.81	13.442%	$182.4261	$182.43	$182.45	$182.40
Purchase #4	$71.62	11.705%	$80.0031	$80.00	$80.00	$80.00
Purchase #5	$42.44	8.460%	$46.0304	$46.03	$46.05	$46.00
Purchase #6	$151.62	4.514%	$158.4641	$158.46	$158.45	$158.50
Purchase #7	$145.58	13.663%	$165.4706	$165.47	$165.45	$165.50
7 purchase totals =	$828.59		$917.3175	$917.31	$917.30	$917.30