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	$80.96	5.612%	$85.5035	$85.50	$85.50	$85.50
Purchase #2	$203.74	9.808%	$223.7228	$223.72	$223.70	$223.70
Purchase #3	$145.39	11.653%	$162.3323	$162.33	$162.35	$162.30
Purchase #4	$36.74	11.289%	$40.8876	$40.89	$40.90	$40.90
Purchase #5	$58.29	6.181%	$61.8929	$61.89	$61.90	$61.90
Purchase #6	$98.76	11.258%	$109.8784	$109.88	$109.90	$109.90
Purchase #7	$9.74	6.852%	$10.4074	$10.41	$10.40	$10.40
7 purchase totals =	$633.62		$694.6249	$694.62	$694.65	$694.60