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	$137.69	6.206%	$146.235	$146.24	$146.25	$146.20
Purchase #2	$37.84	7.402%	$40.6409	$40.64	$40.65	$40.60
Purchase #3	$123.70	5.729%	$130.7868	$130.79	$130.80	$130.80
Purchase #4	$161.60	4.221%	$168.4211	$168.42	$168.40	$168.40
Purchase #5	$197.25	7.573%	$212.1877	$212.19	$212.20	$212.20
Purchase #6	$133.25	7.554%	$143.3157	$143.32	$143.30	$143.30
Purchase #7	$80.64	12.360%	$90.6071	$90.61	$90.60	$90.60
7 purchase totals =	$871.97		$932.1943	$932.21	$932.20	$932.10