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	$124.46	12.870%	$140.478	$140.48	$140.50	$140.50
Purchase #2	$147.31	6.802%	$157.33	$157.33	$157.35	$157.30
Purchase #3	$165.96	3.854%	$172.3561	$172.36	$172.35	$172.40
Purchase #4	$234.39	5.758%	$247.8862	$247.89	$247.90	$247.90
Purchase #5	$239.30	13.658%	$271.9836	$271.98	$272.00	$272.00
Purchase #6	$100.29	9.499%	$109.8165	$109.82	$109.80	$109.80
Purchase #7	$58.87	10.220%	$64.8865	$64.89	$64.90	$64.90
7 purchase totals =	$1,070.58		$1,164.7369	$1,164.75	$1,164.80	$1,164.80