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	$6.86	4.573%	$7.1737	$7.17	$7.15	$7.20
Purchase #2	$227.89	3.493%	$235.8502	$235.85	$235.85	$235.90
Purchase #3	$76.36	5.321%	$80.4231	$80.42	$80.40	$80.40
Purchase #4	$169.52	9.415%	$185.4803	$185.48	$185.50	$185.50
Purchase #5	$78.96	7.827%	$85.1402	$85.14	$85.15	$85.10
Purchase #6	$218.28	9.570%	$239.1694	$239.17	$239.15	$239.20
Purchase #7	$183.70	12.505%	$206.6717	$206.67	$206.65	$206.70
7 purchase totals =	$961.57		$1,039.9086	$1,039.90	$1,039.85	$1,040.00