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	$27.56	3.112%	$28.4177	$28.42	$28.40	$28.40
Purchase #2	$57.45	6.826%	$61.3715	$61.37	$61.35	$61.40
Purchase #3	$216.33	3.456%	$223.8064	$223.81	$223.80	$223.80
Purchase #4	$198.96	6.721%	$212.3321	$212.33	$212.35	$212.30
Purchase #5	$86.70	3.670%	$89.8819	$89.88	$89.90	$89.90
Purchase #6	$170.76	8.250%	$184.8477	$184.85	$184.85	$184.80
Purchase #7	$50.92	11.198%	$56.622	$56.62	$56.60	$56.60
7 purchase totals =	$808.68		$857.2793	$857.28	$857.25	$857.20