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	$33.73	7.807%	$36.3633	$36.36	$36.35	$36.40
Purchase #2	$152.50	6.533%	$162.4628	$162.46	$162.45	$162.50
Purchase #3	$88.67	11.498%	$98.8653	$98.87	$98.85	$98.90
Purchase #4	$72.54	11.735%	$81.0526	$81.05	$81.05	$81.10
Purchase #5	$133.89	7.736%	$144.2477	$144.25	$144.25	$144.20
Purchase #6	$8.52	4.406%	$8.8954	$8.90	$8.90	$8.90
Purchase #7	$114.35	8.386%	$123.9394	$123.94	$123.95	$123.90
7 purchase totals =	$604.20		$655.8265	$655.83	$655.80	$655.90