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	$169.36	11.564%	$188.9448	$188.94	$188.95	$188.90
Purchase #2	$209.66	6.346%	$222.965	$222.97	$222.95	$223.00
Purchase #3	$85.71	7.755%	$92.3568	$92.36	$92.35	$92.40
Purchase #4	$196.53	7.632%	$211.5292	$211.53	$211.55	$211.50
Purchase #5	$94.34	9.332%	$103.1438	$103.14	$103.15	$103.10
Purchase #6	$150.91	9.690%	$165.5332	$165.53	$165.55	$165.50
Purchase #7	$7.94	12.163%	$8.9057	$8.91	$8.90	$8.90
7 purchase totals =	$914.45		$993.3785	$993.38	$993.40	$993.30