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	$229.87	8.854%	$250.2227	$250.22	$250.20	$250.20
Purchase #2	$124.83	12.741%	$140.7346	$140.73	$140.75	$140.70
Purchase #3	$65.43	10.338%	$72.1942	$72.19	$72.20	$72.20
Purchase #4	$203.52	4.330%	$212.3324	$212.33	$212.35	$212.30
Purchase #5	$83.92	10.120%	$92.4127	$92.41	$92.40	$92.40
Purchase #6	$182.76	12.317%	$205.2705	$205.27	$205.25	$205.30
Purchase #7	$112.39	4.330%	$117.2565	$117.26	$117.25	$117.30
7 purchase totals =	$1,002.72		$1,090.4236	$1,090.41	$1,090.40	$1,090.40