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	$16.81	11.345%	$18.7171	$18.72	$18.70	$18.70
Purchase #2	$118.84	7.142%	$127.3276	$127.33	$127.35	$127.30
Purchase #3	$171.33	8.444%	$185.7971	$185.80	$185.80	$185.80
Purchase #4	$158.56	10.572%	$175.323	$175.32	$175.30	$175.30
Purchase #5	$232.79	12.518%	$261.9307	$261.93	$261.95	$261.90
Purchase #6	$200.45	11.417%	$223.3354	$223.34	$223.35	$223.30
Purchase #7	$19.63	7.526%	$21.1074	$21.11	$21.10	$21.10
7 purchase totals =	$918.41		$1,013.5383	$1,013.55	$1,013.55	$1,013.40