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	$123.56	11.151%	$137.3382	$137.34	$137.35	$137.30
Purchase #2	$91.81	10.550%	$101.496	$101.50	$101.50	$101.50
Purchase #3	$200.54	11.620%	$223.8427	$223.84	$223.85	$223.80
Purchase #4	$101.98	9.874%	$112.0495	$112.05	$112.05	$112.00
Purchase #5	$172.93	11.327%	$192.5178	$192.52	$192.50	$192.50
Purchase #6	$143.51	6.352%	$152.6258	$152.63	$152.65	$152.60
Purchase #7	$33.69	9.507%	$36.8929	$36.89	$36.90	$36.90
7 purchase totals =	$868.02		$956.7629	$956.77	$956.80	$956.60