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	3.623%	$28.5585	$28.56	$28.55	$28.60
Purchase #2	$55.71	9.571%	$61.042	$61.04	$61.05	$61.00
Purchase #3	$147.43	3.435%	$152.4942	$152.49	$152.50	$152.50
Purchase #4	$159.41	9.522%	$174.589	$174.59	$174.60	$174.60
Purchase #5	$103.49	5.777%	$109.4686	$109.47	$109.45	$109.50
Purchase #6	$181.76	8.314%	$196.8715	$196.87	$196.85	$196.90
Purchase #7	$116.88	7.717%	$125.8996	$125.90	$125.90	$125.90
7 purchase totals =	$792.24		$848.9234	$848.92	$848.90	$849.00