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	$29.92	3.278%	$30.9008	$30.90	$30.90	$30.90
Purchase #2	$55.42	9.860%	$60.8844	$60.88	$60.90	$60.90
Purchase #3	$140.92	4.537%	$147.3135	$147.31	$147.30	$147.30
Purchase #4	$96.64	6.645%	$103.0617	$103.06	$103.05	$103.10
Purchase #5	$196.69	10.865%	$218.0604	$218.06	$218.05	$218.10
Purchase #6	$228.91	6.495%	$243.7777	$243.78	$243.80	$243.80
Purchase #7	$89.89	11.374%	$100.1141	$100.11	$100.10	$100.10
7 purchase totals =	$838.39		$904.1126	$904.10	$904.10	$904.20