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	$201.91	10.400%	$222.9086	$222.91	$222.90	$222.90
Purchase #2	$207.95	7.707%	$223.9767	$223.98	$224.00	$224.00
Purchase #3	$140.80	11.457%	$156.9315	$156.93	$156.95	$156.90
Purchase #4	$92.80	10.325%	$102.3816	$102.38	$102.40	$102.40
Purchase #5	$73.59	6.740%	$78.55	$78.55	$78.55	$78.60
Purchase #6	$29.33	9.688%	$32.1715	$32.17	$32.15	$32.20
Purchase #7	$105.75	10.843%	$117.2165	$117.22	$117.20	$117.20
7 purchase totals =	$852.13		$934.1364	$934.14	$934.15	$934.20