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	$215.29	11.764%	$240.6167	$240.62	$240.60	$240.60
Purchase #2	$20.26	3.151%	$20.8984	$20.90	$20.90	$20.90
Purchase #3	$33.83	3.489%	$35.0103	$35.01	$35.00	$35.00
Purchase #4	$89.33	10.805%	$98.9821	$98.98	$99.00	$99.00
Purchase #5	$45.44	11.261%	$50.557	$50.56	$50.55	$50.60
Purchase #6	$85.75	4.455%	$89.5702	$89.57	$89.55	$89.60
Purchase #7	$244.47	13.755%	$278.0968	$278.10	$278.10	$278.10
7 purchase totals =	$734.37		$813.7315	$813.74	$813.70	$813.80