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	$148.81	11.433%	$165.8234	$165.82	$165.80	$165.80
Purchase #2	$202.27	9.427%	$221.338	$221.34	$221.35	$221.30
Purchase #3	$195.41	4.552%	$204.3051	$204.31	$204.30	$204.30
Purchase #4	$38.53	13.523%	$43.7404	$43.74	$43.75	$43.70
Purchase #5	$31.51	4.283%	$32.8596	$32.86	$32.85	$32.90
Purchase #6	$98.81	3.315%	$102.0856	$102.09	$102.10	$102.10
Purchase #7	$53.26	12.402%	$59.8653	$59.87	$59.85	$59.90
7 purchase totals =	$768.60		$830.0174	$830.03	$830.00	$830.00