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	$84.69	6.382%	$90.0949	$90.09	$90.10	$90.10
Purchase #2	$101.89	9.116%	$111.1783	$111.18	$111.20	$111.20
Purchase #3	$132.74	11.352%	$147.8086	$147.81	$147.80	$147.80
Purchase #4	$235.85	10.107%	$259.6874	$259.69	$259.70	$259.70
Purchase #5	$85.46	11.648%	$95.4144	$95.41	$95.40	$95.40
Purchase #6	$85.54	12.772%	$96.4652	$96.47	$96.45	$96.50
Purchase #7	$189.43	7.303%	$203.2641	$203.26	$203.25	$203.30
7 purchase totals =	$915.60		$1,003.9129	$1,003.91	$1,003.90	$1,004.00