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	$237.48	12.515%	$267.2006	$267.20	$267.20	$267.20
Purchase #2	$93.96	5.650%	$99.2687	$99.27	$99.25	$99.30
Purchase #3	$50.39	13.484%	$57.1846	$57.18	$57.20	$57.20
Purchase #4	$229.90	13.857%	$261.7572	$261.76	$261.75	$261.80
Purchase #5	$250.29	10.179%	$275.767	$275.77	$275.75	$275.80
Purchase #6	$95.93	4.148%	$99.9092	$99.91	$99.90	$99.90
Purchase #7	$113.56	13.309%	$128.6737	$128.67	$128.65	$128.70
7 purchase totals =	$1,071.51		$1,189.7610	$1,189.76	$1,189.70	$1,189.90