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	$26.59	6.341%	$28.2761	$28.28	$28.30	$28.30
Purchase #2	$229.83	5.527%	$242.5327	$242.53	$242.55	$242.50
Purchase #3	$201.91	11.507%	$225.1438	$225.14	$225.15	$225.10
Purchase #4	$250.57	7.692%	$269.8438	$269.84	$269.85	$269.80
Purchase #5	$73.46	10.683%	$81.3077	$81.31	$81.30	$81.30
Purchase #6	$140.33	7.269%	$150.5306	$150.53	$150.55	$150.50
Purchase #7	$9.81	5.538%	$10.3533	$10.35	$10.35	$10.40
7 purchase totals =	$932.50		$1,007.9880	$1,007.98	$1,008.05	$1,007.90