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	$33.30	7.281%	$35.7246	$35.72	$35.70	$35.70
Purchase #2	$201.36	11.456%	$224.4278	$224.43	$224.45	$224.40
Purchase #3	$73.99	8.731%	$80.4501	$80.45	$80.45	$80.50
Purchase #4	$86.82	3.804%	$90.1226	$90.12	$90.10	$90.10
Purchase #5	$151.38	12.271%	$169.9558	$169.96	$169.95	$170.00
Purchase #6	$130.59	10.777%	$144.6637	$144.66	$144.65	$144.70
Purchase #7	$79.94	8.695%	$86.8908	$86.89	$86.90	$86.90
7 purchase totals =	$757.38		$832.2354	$832.23	$832.20	$832.30