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	$63.48	12.208%	$71.2296	$71.23	$71.25	$71.20
Purchase #2	$56.81	8.124%	$61.4252	$61.43	$61.45	$61.40
Purchase #3	$178.92	3.549%	$185.2699	$185.27	$185.25	$185.30
Purchase #4	$213.90	11.188%	$237.8311	$237.83	$237.85	$237.80
Purchase #5	$99.74	6.475%	$106.1982	$106.20	$106.20	$106.20
Purchase #6	$12.48	7.572%	$13.425	$13.43	$13.45	$13.40
Purchase #7	$223.69	6.581%	$238.411	$238.41	$238.40	$238.40
7 purchase totals =	$849.02		$913.7900	$913.80	$913.85	$913.70