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	$179.73	6.586%	$191.567	$191.57	$191.55	$191.60
Purchase #2	$245.43	8.749%	$266.9027	$266.90	$266.90	$266.90
Purchase #3	$81.93	9.661%	$89.8453	$89.85	$89.85	$89.80
Purchase #4	$182.75	9.586%	$200.2684	$200.27	$200.25	$200.30
Purchase #5	$64.93	13.412%	$73.6384	$73.64	$73.65	$73.60
Purchase #6	$190.59	4.481%	$199.1303	$199.13	$199.15	$199.10
Purchase #7	$96.46	11.303%	$107.3629	$107.36	$107.35	$107.40
7 purchase totals =	$1,041.82		$1,128.7150	$1,128.72	$1,128.70	$1,128.70