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	$171.90	8.419%	$186.3723	$186.37	$186.35	$186.40
Purchase #2	$36.40	6.576%	$38.7937	$38.79	$38.80	$38.80
Purchase #3	$156.59	10.418%	$172.9035	$172.90	$172.90	$172.90
Purchase #4	$184.53	10.299%	$203.5347	$203.53	$203.55	$203.50
Purchase #5	$204.64	11.650%	$228.4806	$228.48	$228.50	$228.50
Purchase #6	$33.79	9.768%	$37.0906	$37.09	$37.10	$37.10
Purchase #7	$98.88	3.445%	$102.2864	$102.29	$102.30	$102.30
7 purchase totals =	$886.73		$969.4618	$969.45	$969.50	$969.50