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	$152.36	13.363%	$172.7199	$172.72	$172.70	$172.70
Purchase #2	$31.69	11.685%	$35.393	$35.39	$35.40	$35.40
Purchase #3	$84.33	6.743%	$90.0164	$90.02	$90.00	$90.00
Purchase #4	$195.47	7.259%	$209.6592	$209.66	$209.65	$209.70
Purchase #5	$118.57	8.585%	$128.7492	$128.75	$128.75	$128.70
Purchase #6	$82.43	5.762%	$87.1796	$87.18	$87.20	$87.20
Purchase #7	$103.88	7.756%	$111.9369	$111.94	$111.95	$111.90
7 purchase totals =	$768.73		$835.6542	$835.66	$835.65	$835.60