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	$71.72	10.343%	$79.138	$79.14	$79.15	$79.10
Purchase #2	$174.73	3.189%	$180.3021	$180.30	$180.30	$180.30
Purchase #3	$72.58	9.590%	$79.5404	$79.54	$79.55	$79.50
Purchase #4	$117.78	11.614%	$131.459	$131.46	$131.45	$131.50
Purchase #5	$138.33	9.760%	$151.831	$151.83	$151.85	$151.80
Purchase #6	$75.66	12.571%	$85.1712	$85.17	$85.15	$85.20
Purchase #7	$140.64	12.838%	$158.6954	$158.70	$158.70	$158.70
7 purchase totals =	$791.44		$866.1371	$866.14	$866.15	$866.10