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	$203.85	12.764%	$229.8694	$229.87	$229.85	$229.90
Purchase #2	$50.36	5.612%	$53.1862	$53.19	$53.20	$53.20
Purchase #3	$55.54	3.183%	$57.3078	$57.31	$57.30	$57.30
Purchase #4	$139.77	8.401%	$151.5121	$151.51	$151.50	$151.50
Purchase #5	$242.41	7.709%	$261.0974	$261.10	$261.10	$261.10
Purchase #6	$38.80	6.173%	$41.1951	$41.20	$41.20	$41.20
Purchase #7	$59.72	13.625%	$67.8569	$67.86	$67.85	$67.90
7 purchase totals =	$790.45		$862.0249	$862.04	$862.00	$862.10