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	$73.86	13.175%	$83.5911	$83.59	$83.60	$83.60
Purchase #2	$128.50	11.797%	$143.6591	$143.66	$143.65	$143.70
Purchase #3	$250.69	7.653%	$269.8753	$269.88	$269.90	$269.90
Purchase #4	$246.55	11.263%	$274.3189	$274.32	$274.30	$274.30
Purchase #5	$96.82	9.170%	$105.6984	$105.70	$105.70	$105.70
Purchase #6	$125.65	4.467%	$131.2628	$131.26	$131.25	$131.30
Purchase #7	$157.66	5.427%	$166.2162	$166.22	$166.20	$166.20
7 purchase totals =	$1,079.73		$1,174.6218	$1,174.63	$1,174.60	$1,174.70