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	$35.86	11.314%	$39.9172	$39.92	$39.90	$39.90
Purchase #2	$71.43	9.671%	$78.338	$78.34	$78.35	$78.30
Purchase #3	$132.62	10.169%	$146.1061	$146.11	$146.10	$146.10
Purchase #4	$31.50	13.704%	$35.8168	$35.82	$35.80	$35.80
Purchase #5	$182.89	9.848%	$200.901	$200.90	$200.90	$200.90
Purchase #6	$125.48	7.806%	$135.275	$135.28	$135.30	$135.30
Purchase #7	$187.73	6.203%	$199.3749	$199.37	$199.35	$199.40
7 purchase totals =	$767.51		$835.7290	$835.74	$835.70	$835.70