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	$31.42	4.664%	$32.8854	$32.89	$32.90	$32.90
Purchase #2	$226.68	10.174%	$249.7424	$249.74	$249.75	$249.70
Purchase #3	$42.81	10.742%	$47.4087	$47.41	$47.40	$47.40
Purchase #4	$194.40	5.765%	$205.6072	$205.61	$205.60	$205.60
Purchase #5	$158.61	13.507%	$180.0335	$180.03	$180.05	$180.00
Purchase #6	$142.96	12.156%	$160.3382	$160.34	$160.35	$160.30
Purchase #7	$71.56	9.319%	$78.2287	$78.23	$78.25	$78.20
7 purchase totals =	$868.44		$954.2441	$954.25	$954.30	$954.10