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	$195.56	9.192%	$213.5359	$213.54	$213.55	$213.50
Purchase #2	$137.69	12.749%	$155.2441	$155.24	$155.25	$155.20
Purchase #3	$51.69	5.508%	$54.5371	$54.54	$54.55	$54.50
Purchase #4	$92.71	12.301%	$104.1143	$104.11	$104.10	$104.10
Purchase #5	$42.84	4.474%	$44.7567	$44.76	$44.75	$44.80
Purchase #6	$92.56	12.121%	$103.7792	$103.78	$103.80	$103.80
Purchase #7	$168.95	3.843%	$175.4427	$175.44	$175.45	$175.40
7 purchase totals =	$782.00		$851.4100	$851.41	$851.45	$851.30