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	$220.84	6.252%	$234.6469	$234.65	$234.65	$234.60
Purchase #2	$104.57	11.498%	$116.5935	$116.59	$116.60	$116.60
Purchase #3	$210.30	6.299%	$223.5468	$223.55	$223.55	$223.50
Purchase #4	$28.33	13.870%	$32.2594	$32.26	$32.25	$32.30
Purchase #5	$236.82	7.131%	$253.7076	$253.71	$253.70	$253.70
Purchase #6	$133.30	11.484%	$148.6082	$148.61	$148.60	$148.60
Purchase #7	$215.48	6.343%	$229.1479	$229.15	$229.15	$229.10
7 purchase totals =	$1,149.64		$1,238.5103	$1,238.52	$1,238.50	$1,238.40