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	$68.75	10.364%	$75.8753	$75.88	$75.90	$75.90
Purchase #2	$113.85	9.503%	$124.6692	$124.67	$124.65	$124.70
Purchase #3	$78.94	13.731%	$89.7793	$89.78	$89.80	$89.80
Purchase #4	$126.71	7.579%	$136.3134	$136.31	$136.30	$136.30
Purchase #5	$141.79	6.281%	$150.6958	$150.70	$150.70	$150.70
Purchase #6	$204.65	10.392%	$225.9172	$225.92	$225.90	$225.90
Purchase #7	$178.56	12.467%	$200.8211	$200.82	$200.80	$200.80
7 purchase totals =	$913.25		$1,004.0713	$1,004.08	$1,004.05	$1,004.10