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	$25.68	8.229%	$27.7932	$27.79	$27.80	$27.80
Purchase #2	$88.98	12.808%	$100.3766	$100.38	$100.40	$100.40
Purchase #3	$209.51	8.786%	$227.9175	$227.92	$227.90	$227.90
Purchase #4	$190.89	13.298%	$216.2746	$216.27	$216.25	$216.30
Purchase #5	$100.65	10.348%	$111.0653	$111.07	$111.05	$111.10
Purchase #6	$243.53	8.433%	$264.0669	$264.07	$264.05	$264.10
Purchase #7	$102.25	12.511%	$115.0425	$115.04	$115.05	$115.00
7 purchase totals =	$961.49		$1,062.5366	$1,062.54	$1,062.50	$1,062.60