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	$93.28	7.411%	$100.193	$100.19	$100.20	$100.20
Purchase #2	$59.56	13.384%	$67.5315	$67.53	$67.55	$67.50
Purchase #3	$58.74	11.860%	$65.7066	$65.71	$65.70	$65.70
Purchase #4	$144.87	5.484%	$152.8147	$152.81	$152.80	$152.80
Purchase #5	$52.91	13.829%	$60.2269	$60.23	$60.25	$60.20
Purchase #6	$139.57	3.290%	$144.1619	$144.16	$144.15	$144.20
Purchase #7	$174.97	8.507%	$189.8547	$189.85	$189.85	$189.90
7 purchase totals =	$723.90		$780.4893	$780.48	$780.50	$780.50