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	$240.66	12.250%	$270.1409	$270.14	$270.15	$270.10
Purchase #2	$114.33	11.269%	$127.2138	$127.21	$127.20	$127.20
Purchase #3	$40.78	5.166%	$42.8867	$42.89	$42.90	$42.90
Purchase #4	$195.62	3.280%	$202.0363	$202.04	$202.05	$202.00
Purchase #5	$10.51	11.825%	$11.7528	$11.75	$11.75	$11.80
Purchase #6	$92.97	8.478%	$100.852	$100.85	$100.85	$100.90
Purchase #7	$64.38	11.445%	$71.7483	$71.75	$71.75	$71.70
7 purchase totals =	$759.25		$826.6308	$826.63	$826.65	$826.60