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	$159.52	5.820%	$168.8041	$168.80	$168.80	$168.80
Purchase #2	$80.93	7.166%	$86.7294	$86.73	$86.75	$86.70
Purchase #3	$221.92	5.528%	$234.1877	$234.19	$234.20	$234.20
Purchase #4	$32.39	4.240%	$33.7633	$33.76	$33.75	$33.80
Purchase #5	$250.26	4.111%	$260.5482	$260.55	$260.55	$260.50
Purchase #6	$79.50	12.411%	$89.3667	$89.37	$89.35	$89.40
Purchase #7	$64.44	12.205%	$72.3049	$72.30	$72.30	$72.30
7 purchase totals =	$888.96		$945.7043	$945.70	$945.70	$945.70