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	$156.83	8.282%	$169.8187	$169.82	$169.80	$169.80
Purchase #2	$149.52	12.805%	$168.666	$168.67	$168.65	$168.70
Purchase #3	$88.53	6.523%	$94.3048	$94.30	$94.30	$94.30
Purchase #4	$243.73	7.308%	$261.5418	$261.54	$261.55	$261.50
Purchase #5	$82.52	3.869%	$85.7127	$85.71	$85.70	$85.70
Purchase #6	$153.30	5.142%	$161.1827	$161.18	$161.20	$161.20
Purchase #7	$141.98	3.803%	$147.3795	$147.38	$147.40	$147.40
7 purchase totals =	$1,016.41		$1,088.6062	$1,088.60	$1,088.60	$1,088.60