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	$37.96	11.610%	$42.3672	$42.37	$42.35	$42.40
Purchase #2	$55.40	5.343%	$58.36	$58.36	$58.35	$58.40
Purchase #3	$36.85	9.292%	$40.2741	$40.27	$40.25	$40.30
Purchase #4	$142.76	7.105%	$152.9031	$152.90	$152.90	$152.90
Purchase #5	$186.51	11.190%	$207.3805	$207.38	$207.40	$207.40
Purchase #6	$28.75	9.607%	$31.512	$31.51	$31.50	$31.50
Purchase #7	$176.51	10.736%	$195.4601	$195.46	$195.45	$195.50
7 purchase totals =	$664.74		$728.2570	$728.25	$728.20	$728.40