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	$36.54	6.279%	$38.8343	$38.83	$38.85	$38.80
Purchase #2	$205.78	9.503%	$225.3353	$225.34	$225.35	$225.30
Purchase #3	$78.61	4.735%	$82.3322	$82.33	$82.35	$82.30
Purchase #4	$85.50	9.572%	$93.6841	$93.68	$93.70	$93.70
Purchase #5	$185.37	7.364%	$199.0206	$199.02	$199.00	$199.00
Purchase #6	$206.35	4.608%	$215.8586	$215.86	$215.85	$215.90
Purchase #7	$216.39	3.726%	$224.4527	$224.45	$224.45	$224.50
7 purchase totals =	$1,014.54		$1,079.5178	$1,079.51	$1,079.55	$1,079.50