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	$63.64	13.336%	$72.127	$72.13	$72.15	$72.10
Purchase #2	$19.99	3.132%	$20.6161	$20.62	$20.60	$20.60
Purchase #3	$28.34	12.386%	$31.8502	$31.85	$31.85	$31.90
Purchase #4	$53.98	8.211%	$58.4123	$58.41	$58.40	$58.40
Purchase #5	$129.96	4.572%	$135.9018	$135.90	$135.90	$135.90
Purchase #6	$227.94	9.829%	$250.3442	$250.34	$250.35	$250.30
Purchase #7	$44.59	12.696%	$50.2511	$50.25	$50.25	$50.30
7 purchase totals =	$568.44		$619.5027	$619.50	$619.50	$619.50