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	$78.96	12.362%	$88.721	$88.72	$88.70	$88.70
Purchase #2	$165.91	8.581%	$180.1467	$180.15	$180.15	$180.10
Purchase #3	$142.45	4.607%	$149.0127	$149.01	$149.00	$149.00
Purchase #4	$47.86	13.576%	$54.3575	$54.36	$54.35	$54.40
Purchase #5	$143.39	6.618%	$152.8796	$152.88	$152.90	$152.90
Purchase #6	$83.79	6.348%	$89.109	$89.11	$89.10	$89.10
Purchase #7	$80.91	6.641%	$86.2832	$86.28	$86.30	$86.30
7 purchase totals =	$743.27		$800.5097	$800.51	$800.50	$800.50