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	$133.90	12.398%	$150.5009	$150.50	$150.50	$150.50
Purchase #2	$83.40	11.414%	$92.9193	$92.92	$92.90	$92.90
Purchase #3	$65.26	12.360%	$73.3261	$73.33	$73.35	$73.30
Purchase #4	$144.35	12.805%	$162.834	$162.83	$162.85	$162.80
Purchase #5	$72.81	7.256%	$78.0931	$78.09	$78.10	$78.10
Purchase #6	$67.77	11.156%	$75.3304	$75.33	$75.35	$75.30
Purchase #7	$164.34	12.264%	$184.4947	$184.49	$184.50	$184.50
7 purchase totals =	$731.83		$817.4985	$817.49	$817.55	$817.40