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	$36.88	9.363%	$40.3331	$40.33	$40.35	$40.30
Purchase #2	$80.25	12.289%	$90.1119	$90.11	$90.10	$90.10
Purchase #3	$80.81	10.483%	$89.2813	$89.28	$89.30	$89.30
Purchase #4	$189.54	8.794%	$206.2081	$206.21	$206.20	$206.20
Purchase #5	$145.53	4.296%	$151.782	$151.78	$151.80	$151.80
Purchase #6	$62.56	13.666%	$71.1094	$71.11	$71.10	$71.10
Purchase #7	$236.76	13.339%	$268.3414	$268.34	$268.35	$268.30
7 purchase totals =	$832.33		$917.1672	$917.16	$917.20	$917.10