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	$124.45	12.529%	$140.0423	$140.04	$140.05	$140.00
Purchase #2	$71.91	8.228%	$77.8268	$77.83	$77.85	$77.80
Purchase #3	$145.73	11.400%	$162.3432	$162.34	$162.35	$162.30
Purchase #4	$135.35	11.850%	$151.389	$151.39	$151.40	$151.40
Purchase #5	$215.57	12.403%	$242.3071	$242.31	$242.30	$242.30
Purchase #6	$123.97	4.718%	$129.8189	$129.82	$129.80	$129.80
Purchase #7	$106.69	5.749%	$112.8236	$112.82	$112.80	$112.80
7 purchase totals =	$923.67		$1,016.5509	$1,016.55	$1,016.55	$1,016.40