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	$20.72	7.359%	$22.2448	$22.24	$22.25	$22.20
Purchase #2	$38.54	9.686%	$42.273	$42.27	$42.25	$42.30
Purchase #3	$150.32	9.543%	$164.665	$164.67	$164.65	$164.70
Purchase #4	$142.49	11.799%	$159.3024	$159.30	$159.30	$159.30
Purchase #5	$92.90	6.776%	$99.1949	$99.19	$99.20	$99.20
Purchase #6	$90.51	11.205%	$100.6516	$100.65	$100.65	$100.70
Purchase #7	$67.69	7.695%	$72.8987	$72.90	$72.90	$72.90
7 purchase totals =	$603.17		$661.2304	$661.22	$661.20	$661.30