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	$53.97	4.146%	$56.2076	$56.21	$56.20	$56.20
Purchase #2	$161.94	12.705%	$182.5145	$182.51	$182.50	$182.50
Purchase #3	$225.65	11.158%	$250.828	$250.83	$250.85	$250.80
Purchase #4	$212.38	7.541%	$228.3956	$228.40	$228.40	$228.40
Purchase #5	$98.67	4.818%	$103.4239	$103.42	$103.40	$103.40
Purchase #6	$150.56	5.780%	$159.2624	$159.26	$159.25	$159.30
Purchase #7	$81.96	11.259%	$91.1879	$91.19	$91.20	$91.20
7 purchase totals =	$985.13		$1,071.8199	$1,071.82	$1,071.80	$1,071.80