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	$135.98	12.135%	$152.4812	$152.48	$152.50	$152.50
Purchase #2	$104.78	4.762%	$109.7696	$109.77	$109.75	$109.80
Purchase #3	$150.48	9.594%	$164.9171	$164.92	$164.90	$164.90
Purchase #4	$147.88	8.368%	$160.2546	$160.25	$160.25	$160.30
Purchase #5	$84.27	13.796%	$95.8959	$95.90	$95.90	$95.90
Purchase #6	$219.91	10.327%	$242.6201	$242.62	$242.60	$242.60
Purchase #7	$28.95	8.250%	$31.3384	$31.34	$31.35	$31.30
7 purchase totals =	$872.25		$957.2769	$957.28	$957.25	$957.30