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	$235.89	6.288%	$250.7228	$250.72	$250.70	$250.70
Purchase #2	$235.42	4.753%	$246.6095	$246.61	$246.60	$246.60
Purchase #3	$85.58	4.465%	$89.4011	$89.40	$89.40	$89.40
Purchase #4	$122.86	11.406%	$136.8734	$136.87	$136.85	$136.90
Purchase #5	$178.97	9.393%	$195.7807	$195.78	$195.80	$195.80
Purchase #6	$171.69	5.187%	$180.5956	$180.60	$180.60	$180.60
Purchase #7	$74.54	8.300%	$80.7268	$80.73	$80.75	$80.70
7 purchase totals =	$1,104.95		$1,180.7099	$1,180.71	$1,180.70	$1,180.70