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	$21.79	12.726%	$24.563	$24.56	$24.55	$24.60
Purchase #2	$37.28	13.438%	$42.2897	$42.29	$42.30	$42.30
Purchase #3	$148.54	9.471%	$162.6082	$162.61	$162.60	$162.60
Purchase #4	$244.73	10.868%	$271.3273	$271.33	$271.35	$271.30
Purchase #5	$125.32	13.172%	$141.8272	$141.83	$141.85	$141.80
Purchase #6	$208.41	13.441%	$236.4224	$236.42	$236.40	$236.40
Purchase #7	$41.59	12.756%	$46.8952	$46.90	$46.90	$46.90
7 purchase totals =	$827.66		$925.9330	$925.94	$925.95	$925.90