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	$55.60	4.853%	$58.2983	$58.30	$58.30	$58.30
Purchase #2	$218.86	6.427%	$232.9261	$232.93	$232.95	$232.90
Purchase #3	$140.83	5.761%	$148.9432	$148.94	$148.95	$148.90
Purchase #4	$150.55	7.751%	$162.2191	$162.22	$162.20	$162.20
Purchase #5	$37.53	8.548%	$40.7381	$40.74	$40.75	$40.70
Purchase #6	$78.89	6.246%	$83.8175	$83.82	$83.80	$83.80
Purchase #7	$96.34	3.727%	$99.9306	$99.93	$99.95	$99.90
7 purchase totals =	$778.60		$826.8729	$826.88	$826.90	$826.70