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	$32.44	13.624%	$36.8596	$36.86	$36.85	$36.90
Purchase #2	$55.97	6.336%	$59.5163	$59.52	$59.50	$59.50
Purchase #3	$41.33	13.236%	$46.8004	$46.80	$46.80	$46.80
Purchase #4	$191.31	13.166%	$216.4979	$216.50	$216.50	$216.50
Purchase #5	$116.28	6.221%	$123.5138	$123.51	$123.50	$123.50
Purchase #6	$8.33	5.560%	$8.7931	$8.79	$8.80	$8.80
Purchase #7	$6.85	7.347%	$7.3533	$7.35	$7.35	$7.40
7 purchase totals =	$452.51		$499.3344	$499.33	$499.30	$499.40