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	$139.70	4.581%	$146.0997	$146.10	$146.10	$146.10
Purchase #2	$144.72	4.682%	$151.4958	$151.50	$151.50	$151.50
Purchase #3	$221.76	8.453%	$240.5054	$240.51	$240.50	$240.50
Purchase #4	$145.41	4.389%	$151.792	$151.79	$151.80	$151.80
Purchase #5	$249.72	4.565%	$261.1197	$261.12	$261.10	$261.10
Purchase #6	$92.63	10.409%	$102.2719	$102.27	$102.25	$102.30
Purchase #7	$37.48	6.556%	$39.9372	$39.94	$39.95	$39.90
7 purchase totals =	$1,031.42		$1,093.2217	$1,093.23	$1,093.20	$1,093.20