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	$119.59	13.164%	$135.3328	$135.33	$135.35	$135.30
Purchase #2	$181.31	5.698%	$191.641	$191.64	$191.65	$191.60
Purchase #3	$74.77	10.340%	$82.5012	$82.50	$82.50	$82.50
Purchase #4	$84.57	13.694%	$96.151	$96.15	$96.15	$96.20
Purchase #5	$104.58	4.742%	$109.5392	$109.54	$109.55	$109.50
Purchase #6	$144.78	11.564%	$161.5224	$161.52	$161.50	$161.50
Purchase #7	$55.94	9.414%	$61.2062	$61.21	$61.20	$61.20
7 purchase totals =	$765.54		$837.8938	$837.89	$837.90	$837.80