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	$130.31	9.663%	$142.9019	$142.90	$142.90	$142.90
Purchase #2	$40.54	12.457%	$45.5901	$45.59	$45.60	$45.60
Purchase #3	$93.61	7.224%	$100.3724	$100.37	$100.35	$100.40
Purchase #4	$137.42	3.279%	$141.926	$141.93	$141.95	$141.90
Purchase #5	$48.32	3.641%	$50.0793	$50.08	$50.10	$50.10
Purchase #6	$93.50	5.561%	$98.6995	$98.70	$98.70	$98.70
Purchase #7	$86.64	6.346%	$92.1382	$92.14	$92.15	$92.10
7 purchase totals =	$630.34		$671.7074	$671.71	$671.75	$671.70