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	$55.58	6.705%	$59.3066	$59.31	$59.30	$59.30
Purchase #2	$181.53	10.137%	$199.9317	$199.93	$199.95	$199.90
Purchase #3	$166.56	9.638%	$182.6131	$182.61	$182.60	$182.60
Purchase #4	$86.28	10.446%	$95.2928	$95.29	$95.30	$95.30
Purchase #5	$50.79	9.503%	$55.6166	$55.62	$55.60	$55.60
Purchase #6	$89.93	6.267%	$95.5659	$95.57	$95.55	$95.60
Purchase #7	$76.73	10.829%	$85.0391	$85.04	$85.05	$85.00
7 purchase totals =	$707.40		$773.3658	$773.37	$773.35	$773.30