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	$90.41	3.232%	$93.3321	$93.33	$93.35	$93.30
Purchase #2	$87.81	7.413%	$94.3194	$94.32	$94.30	$94.30
Purchase #3	$39.35	7.124%	$42.1533	$42.15	$42.15	$42.20
Purchase #4	$39.78	6.127%	$42.2173	$42.22	$42.20	$42.20
Purchase #5	$185.60	9.319%	$202.8961	$202.90	$202.90	$202.90
Purchase #6	$31.54	6.732%	$33.6633	$33.66	$33.65	$33.70
Purchase #7	$151.69	8.408%	$164.4441	$164.44	$164.45	$164.40
7 purchase totals =	$626.18		$673.0256	$673.02	$673.00	$673.00