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	$234.27	3.770%	$243.102	$243.10	$243.10	$243.10
Purchase #2	$139.42	8.687%	$151.5314	$151.53	$151.55	$151.50
Purchase #3	$121.82	7.181%	$130.5679	$130.57	$130.55	$130.60
Purchase #4	$158.26	5.409%	$166.8203	$166.82	$166.80	$166.80
Purchase #5	$210.86	5.490%	$222.4362	$222.44	$222.45	$222.40
Purchase #6	$205.54	8.618%	$223.2534	$223.25	$223.25	$223.30
Purchase #7	$93.97	6.681%	$100.2481	$100.25	$100.25	$100.20
7 purchase totals =	$1,164.14		$1,237.9593	$1,237.96	$1,237.95	$1,237.90