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	$66.76	13.713%	$75.9148	$75.91	$75.90	$75.90
Purchase #2	$154.31	7.796%	$166.34	$166.34	$166.35	$166.30
Purchase #3	$150.80	7.433%	$162.009	$162.01	$162.00	$162.00
Purchase #4	$36.45	11.199%	$40.532	$40.53	$40.55	$40.50
Purchase #5	$190.87	9.644%	$209.2775	$209.28	$209.30	$209.30
Purchase #6	$57.65	9.280%	$62.9999	$63.00	$63.00	$63.00
Purchase #7	$40.33	13.736%	$45.8697	$45.87	$45.85	$45.90
7 purchase totals =	$697.17		$762.9429	$762.94	$762.95	$762.90