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	$79.91	4.649%	$83.625	$83.63	$83.65	$83.60
Purchase #2	$58.95	4.147%	$61.3947	$61.39	$61.40	$61.40
Purchase #3	$241.38	3.802%	$250.5573	$250.56	$250.55	$250.60
Purchase #4	$144.50	12.234%	$162.1781	$162.18	$162.20	$162.20
Purchase #5	$66.37	10.782%	$73.526	$73.53	$73.55	$73.50
Purchase #6	$140.98	3.868%	$146.4331	$146.43	$146.45	$146.40
Purchase #7	$85.72	7.850%	$92.449	$92.45	$92.45	$92.40
7 purchase totals =	$817.81		$870.1632	$870.17	$870.25	$870.10