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	$78.88	13.436%	$89.4783	$89.48	$89.50	$89.50
Purchase #2	$227.61	11.739%	$254.3291	$254.33	$254.35	$254.30
Purchase #3	$73.31	9.828%	$80.5149	$80.51	$80.50	$80.50
Purchase #4	$211.89	11.528%	$236.3167	$236.32	$236.30	$236.30
Purchase #5	$207.43	12.276%	$232.8941	$232.89	$232.90	$232.90
Purchase #6	$94.49	7.746%	$101.8092	$101.81	$101.80	$101.80
Purchase #7	$77.44	13.468%	$87.8696	$87.87	$87.85	$87.90
7 purchase totals =	$971.05		$1,083.2119	$1,083.21	$1,083.20	$1,083.20