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	$90.89	12.555%	$102.3012	$102.30	$102.30	$102.30
Purchase #2	$209.54	3.488%	$216.8488	$216.85	$216.85	$216.80
Purchase #3	$119.82	11.421%	$133.5046	$133.50	$133.50	$133.50
Purchase #4	$152.48	11.396%	$169.8566	$169.86	$169.85	$169.90
Purchase #5	$171.47	5.614%	$181.0963	$181.10	$181.10	$181.10
Purchase #6	$56.34	5.822%	$59.6201	$59.62	$59.60	$59.60
Purchase #7	$201.63	8.717%	$219.2061	$219.21	$219.20	$219.20
7 purchase totals =	$1,002.17		$1,082.4337	$1,082.44	$1,082.40	$1,082.40