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	$135.25	4.390%	$141.1875	$141.19	$141.20	$141.20
Purchase #2	$96.72	4.325%	$100.9031	$100.90	$100.90	$100.90
Purchase #3	$79.34	3.473%	$82.0955	$82.10	$82.10	$82.10
Purchase #4	$111.90	5.541%	$118.1004	$118.10	$118.10	$118.10
Purchase #5	$18.85	5.218%	$19.8336	$19.83	$19.85	$19.80
Purchase #6	$59.88	12.415%	$67.3141	$67.31	$67.30	$67.30
Purchase #7	$234.61	6.644%	$250.1975	$250.20	$250.20	$250.20
7 purchase totals =	$736.55		$779.6317	$779.63	$779.65	$779.60