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	$26.48	6.218%	$28.1265	$28.13	$28.15	$28.10
Purchase #2	$110.53	7.224%	$118.5147	$118.51	$118.50	$118.50
Purchase #3	$200.96	4.164%	$209.328	$209.33	$209.35	$209.30
Purchase #4	$112.96	3.146%	$116.5137	$116.51	$116.50	$116.50
Purchase #5	$67.91	7.460%	$72.9761	$72.98	$73.00	$73.00
Purchase #6	$113.28	10.148%	$124.7757	$124.78	$124.80	$124.80
Purchase #7	$164.47	13.703%	$187.0073	$187.01	$187.00	$187.00
7 purchase totals =	$796.59		$857.2420	$857.25	$857.30	$857.20