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	$92.97	7.488%	$99.9316	$99.93	$99.95	$99.90
Purchase #2	$243.45	8.464%	$264.0556	$264.06	$264.05	$264.10
Purchase #3	$203.83	9.470%	$223.1327	$223.13	$223.15	$223.10
Purchase #4	$27.37	5.465%	$28.8658	$28.87	$28.85	$28.90
Purchase #5	$175.25	3.767%	$181.8517	$181.85	$181.85	$181.90
Purchase #6	$47.56	8.451%	$51.5793	$51.58	$51.60	$51.60
Purchase #7	$223.72	5.658%	$236.3781	$236.38	$236.40	$236.40
7 purchase totals =	$1,014.15		$1,085.7948	$1,085.80	$1,085.85	$1,085.90