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	$245.70	3.511%	$254.3265	$254.33	$254.35	$254.30
Purchase #2	$29.42	6.511%	$31.3355	$31.34	$31.35	$31.30
Purchase #3	$213.55	11.732%	$238.6037	$238.60	$238.60	$238.60
Purchase #4	$77.82	3.391%	$80.4589	$80.46	$80.45	$80.50
Purchase #5	$241.71	9.770%	$265.3251	$265.33	$265.35	$265.30
Purchase #6	$225.69	5.781%	$238.7371	$238.74	$238.75	$238.70
Purchase #7	$161.83	3.661%	$167.7546	$167.75	$167.75	$167.80
7 purchase totals =	$1,195.72		$1,276.5414	$1,276.55	$1,276.60	$1,276.50