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	$168.74	12.494%	$189.8224	$189.82	$189.80	$189.80
Purchase #2	$52.76	5.305%	$55.5589	$55.56	$55.55	$55.60
Purchase #3	$179.78	7.266%	$192.8428	$192.84	$192.85	$192.80
Purchase #4	$55.59	7.256%	$59.6236	$59.62	$59.60	$59.60
Purchase #5	$249.52	6.375%	$265.4269	$265.43	$265.45	$265.40
Purchase #6	$188.78	12.632%	$212.6267	$212.63	$212.65	$212.60
Purchase #7	$52.90	6.394%	$56.2824	$56.28	$56.30	$56.30
7 purchase totals =	$948.07		$1,032.1837	$1,032.18	$1,032.20	$1,032.10