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	$117.25	11.818%	$131.1066	$131.11	$131.10	$131.10
Purchase #2	$153.54	11.453%	$171.1249	$171.12	$171.10	$171.10
Purchase #3	$94.59	6.703%	$100.9304	$100.93	$100.95	$100.90
Purchase #4	$113.51	9.385%	$124.1629	$124.16	$124.15	$124.20
Purchase #5	$6.90	4.237%	$7.1924	$7.19	$7.20	$7.20
Purchase #6	$27.72	3.154%	$28.5943	$28.59	$28.60	$28.60
Purchase #7	$22.55	11.766%	$25.2032	$25.20	$25.20	$25.20
7 purchase totals =	$536.06		$588.3147	$588.30	$588.30	$588.30