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	$107.35	13.340%	$121.6705	$121.67	$121.65	$121.70
Purchase #2	$199.32	9.705%	$218.664	$218.66	$218.65	$218.70
Purchase #3	$135.95	4.327%	$141.8326	$141.83	$141.85	$141.80
Purchase #4	$243.40	8.181%	$263.3126	$263.31	$263.30	$263.30
Purchase #5	$79.68	13.851%	$90.7165	$90.72	$90.70	$90.70
Purchase #6	$87.85	3.483%	$90.9098	$90.91	$90.90	$90.90
Purchase #7	$78.66	5.246%	$82.7865	$82.79	$82.80	$82.80
7 purchase totals =	$932.21		$1,009.8925	$1,009.89	$1,009.85	$1,009.90