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	$35.70	9.659%	$39.1483	$39.15	$39.15	$39.10
Purchase #2	$89.88	10.274%	$99.1143	$99.11	$99.10	$99.10
Purchase #3	$75.26	9.338%	$82.2878	$82.29	$82.30	$82.30
Purchase #4	$141.53	5.392%	$149.1613	$149.16	$149.15	$149.20
Purchase #5	$98.38	10.531%	$108.7404	$108.74	$108.75	$108.70
Purchase #6	$134.33	5.494%	$141.7101	$141.71	$141.70	$141.70
Purchase #7	$7.56	7.751%	$8.146	$8.15	$8.15	$8.10
7 purchase totals =	$582.64		$628.3082	$628.31	$628.30	$628.20