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	$145.34	6.362%	$154.5865	$154.59	$154.60	$154.60
Purchase #2	$189.79	12.466%	$213.4492	$213.45	$213.45	$213.40
Purchase #3	$71.44	9.124%	$77.9582	$77.96	$77.95	$78.00
Purchase #4	$219.47	9.479%	$240.2736	$240.27	$240.25	$240.30
Purchase #5	$209.95	6.402%	$223.391	$223.39	$223.40	$223.40
Purchase #6	$242.54	10.275%	$267.461	$267.46	$267.45	$267.50
Purchase #7	$87.63	13.648%	$99.5897	$99.59	$99.60	$99.60
7 purchase totals =	$1,166.16		$1,276.7092	$1,276.71	$1,276.70	$1,276.80