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	$250.48	12.438%	$281.6347	$281.63	$281.65	$281.60
Purchase #2	$202.89	10.340%	$223.8688	$223.87	$223.85	$223.90
Purchase #3	$54.67	8.330%	$59.224	$59.22	$59.20	$59.20
Purchase #4	$202.87	9.867%	$222.8872	$222.89	$222.90	$222.90
Purchase #5	$225.81	12.227%	$253.4198	$253.42	$253.40	$253.40
Purchase #6	$77.73	12.711%	$87.6103	$87.61	$87.60	$87.60
Purchase #7	$180.33	10.797%	$199.8002	$199.80	$199.80	$199.80
7 purchase totals =	$1,194.78		$1,328.4450	$1,328.44	$1,328.40	$1,328.40