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	$83.30	10.315%	$91.8924	$91.89	$91.90	$91.90
Purchase #2	$91.87	10.342%	$101.3712	$101.37	$101.35	$101.40
Purchase #3	$98.63	7.594%	$106.12	$106.12	$106.10	$106.10
Purchase #4	$78.55	13.868%	$89.4433	$89.44	$89.45	$89.40
Purchase #5	$78.88	12.615%	$88.8307	$88.83	$88.85	$88.80
Purchase #6	$68.46	12.185%	$76.8019	$76.80	$76.80	$76.80
Purchase #7	$42.77	7.573%	$46.009	$46.01	$46.00	$46.00
7 purchase totals =	$542.46		$600.4685	$600.46	$600.45	$600.40