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	$198.41	12.611%	$223.4315	$223.43	$223.45	$223.40
Purchase #2	$143.74	11.560%	$160.3563	$160.36	$160.35	$160.40
Purchase #3	$240.39	12.589%	$270.6527	$270.65	$270.65	$270.70
Purchase #4	$79.50	12.300%	$89.2785	$89.28	$89.30	$89.30
Purchase #5	$93.59	11.316%	$104.1806	$104.18	$104.20	$104.20
Purchase #6	$137.99	10.807%	$152.9026	$152.90	$152.90	$152.90
Purchase #7	$147.54	12.431%	$165.8807	$165.88	$165.90	$165.90
7 purchase totals =	$1,041.16		$1,166.6829	$1,166.68	$1,166.75	$1,166.80