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	$235.57	5.281%	$248.0105	$248.01	$248.00	$248.00
Purchase #2	$94.58	12.512%	$106.4138	$106.41	$106.40	$106.40
Purchase #3	$166.92	7.498%	$179.4357	$179.44	$179.45	$179.40
Purchase #4	$96.51	13.325%	$109.37	$109.37	$109.35	$109.40
Purchase #5	$128.72	11.464%	$143.4765	$143.48	$143.50	$143.50
Purchase #6	$143.67	4.633%	$150.3262	$150.33	$150.35	$150.30
Purchase #7	$100.31	3.360%	$103.6804	$103.68	$103.70	$103.70
7 purchase totals =	$966.28		$1,040.7131	$1,040.72	$1,040.75	$1,040.70