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	$109.40	6.817%	$116.8578	$116.86	$116.85	$116.90
Purchase #2	$17.76	4.432%	$18.5471	$18.55	$18.55	$18.50
Purchase #3	$53.67	8.690%	$58.3339	$58.33	$58.35	$58.30
Purchase #4	$55.40	6.531%	$59.0182	$59.02	$59.00	$59.00
Purchase #5	$228.96	6.761%	$244.44	$244.44	$244.45	$244.40
Purchase #6	$69.60	4.579%	$72.787	$72.79	$72.80	$72.80
Purchase #7	$85.59	5.765%	$90.5243	$90.52	$90.50	$90.50
7 purchase totals =	$620.38		$660.5083	$660.51	$660.50	$660.40