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	$106.59	3.584%	$110.4102	$110.41	$110.40	$110.40
Purchase #2	$141.56	3.708%	$146.809	$146.81	$146.80	$146.80
Purchase #3	$168.94	11.839%	$188.9408	$188.94	$188.95	$188.90
Purchase #4	$109.85	5.530%	$115.9247	$115.92	$115.90	$115.90
Purchase #5	$169.26	12.744%	$190.8305	$190.83	$190.85	$190.80
Purchase #6	$12.81	10.454%	$14.1492	$14.15	$14.15	$14.10
Purchase #7	$114.72	7.269%	$123.059	$123.06	$123.05	$123.10
7 purchase totals =	$823.73		$890.1234	$890.12	$890.10	$890.00