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	$88.72	3.837%	$92.1242	$92.12	$92.10	$92.10
Purchase #2	$100.84	10.426%	$111.3536	$111.35	$111.35	$111.40
Purchase #3	$200.88	3.821%	$208.5556	$208.56	$208.55	$208.60
Purchase #4	$196.65	7.325%	$211.0546	$211.05	$211.05	$211.10
Purchase #5	$39.41	3.789%	$40.9032	$40.90	$40.90	$40.90
Purchase #6	$168.68	4.355%	$176.026	$176.03	$176.05	$176.00
Purchase #7	$22.80	13.740%	$25.9327	$25.93	$25.95	$25.90
7 purchase totals =	$817.98		$865.9499	$865.94	$865.95	$866.00