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	$91.59	8.449%	$99.3284	$99.33	$99.35	$99.30
Purchase #2	$189.67	8.303%	$205.4183	$205.42	$205.40	$205.40
Purchase #3	$165.83	6.451%	$176.5277	$176.53	$176.55	$176.50
Purchase #4	$34.61	3.482%	$35.8151	$35.82	$35.80	$35.80
Purchase #5	$24.44	12.323%	$27.4517	$27.45	$27.45	$27.50
Purchase #6	$245.94	11.779%	$274.9093	$274.91	$274.90	$274.90
Purchase #7	$172.40	4.581%	$180.2976	$180.30	$180.30	$180.30
7 purchase totals =	$924.48		$999.7481	$999.76	$999.75	$999.70