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	$82.54	9.507%	$90.3871	$90.39	$90.40	$90.40
Purchase #2	$235.90	6.120%	$250.3371	$250.34	$250.35	$250.30
Purchase #3	$229.74	7.451%	$246.8579	$246.86	$246.85	$246.90
Purchase #4	$205.65	7.424%	$220.9175	$220.92	$220.90	$220.90
Purchase #5	$53.69	6.722%	$57.299	$57.30	$57.30	$57.30
Purchase #6	$78.55	12.761%	$88.5738	$88.57	$88.55	$88.60
Purchase #7	$37.43	12.859%	$42.2431	$42.24	$42.25	$42.20
7 purchase totals =	$923.50		$996.6155	$996.62	$996.60	$996.60