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	$20.38	4.197%	$21.2353	$21.24	$21.25	$21.20
Purchase #2	$79.59	8.355%	$86.2397	$86.24	$86.25	$86.20
Purchase #3	$80.52	12.815%	$90.8386	$90.84	$90.85	$90.80
Purchase #4	$221.48	5.694%	$234.0911	$234.09	$234.10	$234.10
Purchase #5	$72.85	13.270%	$82.5172	$82.52	$82.50	$82.50
Purchase #6	$149.29	6.736%	$159.3462	$159.35	$159.35	$159.30
Purchase #7	$87.34	10.454%	$96.4705	$96.47	$96.45	$96.50
7 purchase totals =	$711.45		$770.7386	$770.75	$770.75	$770.60