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	$129.43	8.558%	$140.5066	$140.51	$140.50	$140.50
Purchase #2	$76.74	10.860%	$85.074	$85.07	$85.05	$85.10
Purchase #3	$89.54	6.635%	$95.481	$95.48	$95.50	$95.50
Purchase #4	$244.61	8.601%	$265.6489	$265.65	$265.65	$265.60
Purchase #5	$162.45	9.498%	$177.8795	$177.88	$177.90	$177.90
Purchase #6	$184.81	8.689%	$200.8681	$200.87	$200.85	$200.90
Purchase #7	$67.73	10.409%	$74.78	$74.78	$74.80	$74.80
7 purchase totals =	$955.31		$1,040.2381	$1,040.24	$1,040.25	$1,040.30