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	$167.96	13.317%	$190.3272	$190.33	$190.35	$190.30
Purchase #2	$50.51	8.552%	$54.8296	$54.83	$54.85	$54.80
Purchase #3	$148.44	13.365%	$168.279	$168.28	$168.30	$168.30
Purchase #4	$181.72	10.267%	$200.3772	$200.38	$200.40	$200.40
Purchase #5	$89.43	9.685%	$98.0913	$98.09	$98.10	$98.10
Purchase #6	$76.51	11.735%	$85.4884	$85.49	$85.50	$85.50
Purchase #7	$30.59	10.269%	$33.7313	$33.73	$33.75	$33.70
7 purchase totals =	$745.16		$831.1240	$831.13	$831.25	$831.10