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	$95.33	8.648%	$103.5741	$103.57	$103.55	$103.60
Purchase #2	$81.36	12.122%	$91.2225	$91.22	$91.20	$91.20
Purchase #3	$110.94	11.626%	$123.8379	$123.84	$123.85	$123.80
Purchase #4	$67.27	7.154%	$72.0825	$72.08	$72.10	$72.10
Purchase #5	$131.54	11.267%	$146.3606	$146.36	$146.35	$146.40
Purchase #6	$135.56	6.541%	$144.427	$144.43	$144.45	$144.40
Purchase #7	$80.74	5.150%	$84.8981	$84.90	$84.90	$84.90
7 purchase totals =	$702.74		$766.4027	$766.40	$766.40	$766.40