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	$125.80	13.180%	$142.3804	$142.38	$142.40	$142.40
Purchase #2	$110.75	5.363%	$116.6895	$116.69	$116.70	$116.70
Purchase #3	$184.45	12.178%	$206.9123	$206.91	$206.90	$206.90
Purchase #4	$36.34	4.222%	$37.8743	$37.87	$37.85	$37.90
Purchase #5	$204.38	13.469%	$231.9079	$231.91	$231.90	$231.90
Purchase #6	$124.87	13.802%	$142.1046	$142.10	$142.10	$142.10
Purchase #7	$169.76	11.312%	$188.9633	$188.96	$188.95	$189.00
7 purchase totals =	$956.35		$1,066.8323	$1,066.82	$1,066.80	$1,066.90