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	$244.64	10.639%	$270.6672	$270.67	$270.65	$270.70
Purchase #2	$160.82	7.152%	$172.3218	$172.32	$172.30	$172.30
Purchase #3	$136.76	11.516%	$152.5093	$152.51	$152.50	$152.50
Purchase #4	$232.96	9.499%	$255.0889	$255.09	$255.10	$255.10
Purchase #5	$7.66	6.780%	$8.1793	$8.18	$8.20	$8.20
Purchase #6	$175.99	9.293%	$192.3448	$192.34	$192.35	$192.30
Purchase #7	$185.32	8.342%	$200.7794	$200.78	$200.80	$200.80
7 purchase totals =	$1,144.15		$1,251.8907	$1,251.89	$1,251.90	$1,251.90