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	$11.98	6.468%	$12.7549	$12.75	$12.75	$12.80
Purchase #2	$99.31	10.392%	$109.6303	$109.63	$109.65	$109.60
Purchase #3	$194.82	12.453%	$219.0809	$219.08	$219.10	$219.10
Purchase #4	$173.30	9.645%	$190.0148	$190.01	$190.00	$190.00
Purchase #5	$83.34	10.259%	$91.8899	$91.89	$91.90	$91.90
Purchase #6	$41.81	8.231%	$45.2514	$45.25	$45.25	$45.30
Purchase #7	$39.31	10.121%	$43.2886	$43.29	$43.30	$43.30
7 purchase totals =	$643.87		$711.9108	$711.90	$711.95	$712.00