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	$50.96	6.599%	$54.3229	$54.32	$54.30	$54.30
Purchase #2	$82.89	12.467%	$93.2239	$93.22	$93.20	$93.20
Purchase #3	$34.90	7.145%	$37.3936	$37.39	$37.40	$37.40
Purchase #4	$245.46	9.184%	$268.003	$268.00	$268.00	$268.00
Purchase #5	$169.90	12.369%	$190.9149	$190.91	$190.90	$190.90
Purchase #6	$138.42	11.191%	$153.9106	$153.91	$153.90	$153.90
Purchase #7	$170.48	11.573%	$190.2097	$190.21	$190.20	$190.20
7 purchase totals =	$893.01		$987.9786	$987.96	$987.90	$987.90