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	$113.89	3.526%	$117.9058	$117.91	$117.90	$117.90
Purchase #2	$134.95	7.389%	$144.9215	$144.92	$144.90	$144.90
Purchase #3	$102.31	9.725%	$112.2596	$112.26	$112.25	$112.30
Purchase #4	$146.60	10.674%	$162.2481	$162.25	$162.25	$162.20
Purchase #5	$110.67	6.725%	$118.1126	$118.11	$118.10	$118.10
Purchase #6	$229.27	6.371%	$243.8768	$243.88	$243.90	$243.90
Purchase #7	$130.52	7.448%	$140.2411	$140.24	$140.25	$140.20
7 purchase totals =	$968.21		$1,039.5655	$1,039.57	$1,039.55	$1,039.50