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	$29.79	4.221%	$31.0474	$31.05	$31.05	$31.00
Purchase #2	$52.36	13.240%	$59.2925	$59.29	$59.30	$59.30
Purchase #3	$59.75	11.203%	$66.4438	$66.44	$66.45	$66.40
Purchase #4	$33.31	12.188%	$37.3698	$37.37	$37.35	$37.40
Purchase #5	$76.73	6.768%	$81.9231	$81.92	$81.90	$81.90
Purchase #6	$73.34	11.858%	$82.0367	$82.04	$82.05	$82.00
Purchase #7	$83.59	11.563%	$93.2555	$93.26	$93.25	$93.30
7 purchase totals =	$408.87		$451.3688	$451.37	$451.35	$451.30