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	$244.78	4.279%	$255.2541	$255.25	$255.25	$255.30
Purchase #2	$60.51	13.659%	$68.7751	$68.78	$68.80	$68.80
Purchase #3	$140.97	9.475%	$154.3269	$154.33	$154.35	$154.30
Purchase #4	$182.80	4.426%	$190.8907	$190.89	$190.90	$190.90
Purchase #5	$130.31	4.560%	$136.2521	$136.25	$136.25	$136.30
Purchase #6	$85.82	12.511%	$96.5569	$96.56	$96.55	$96.60
Purchase #7	$67.66	13.419%	$76.7393	$76.74	$76.75	$76.70
7 purchase totals =	$912.85		$978.7951	$978.80	$978.85	$978.90