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	$52.84	12.189%	$59.2807	$59.28	$59.30	$59.30
Purchase #2	$242.77	12.497%	$273.109	$273.11	$273.10	$273.10
Purchase #3	$232.80	6.334%	$247.5456	$247.55	$247.55	$247.50
Purchase #4	$43.48	6.554%	$46.3297	$46.33	$46.35	$46.30
Purchase #5	$230.34	10.516%	$254.5626	$254.56	$254.55	$254.60
Purchase #6	$30.53	5.231%	$32.127	$32.13	$32.15	$32.10
Purchase #7	$80.44	4.220%	$83.8346	$83.83	$83.85	$83.80
7 purchase totals =	$913.20		$996.7892	$996.79	$996.85	$996.70