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	$101.51	3.763%	$105.3298	$105.33	$105.35	$105.30
Purchase #2	$192.41	9.696%	$211.0661	$211.07	$211.05	$211.10
Purchase #3	$152.70	9.191%	$166.7347	$166.73	$166.75	$166.70
Purchase #4	$80.37	5.769%	$85.0065	$85.01	$85.00	$85.00
Purchase #5	$154.94	8.504%	$168.1161	$168.12	$168.10	$168.10
Purchase #6	$86.96	4.832%	$91.1619	$91.16	$91.15	$91.20
Purchase #7	$39.93	7.218%	$42.8121	$42.81	$42.80	$42.80
7 purchase totals =	$808.82		$870.2272	$870.23	$870.20	$870.20