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	$28.95	10.142%	$31.8861	$31.89	$31.90	$31.90
Purchase #2	$90.47	7.395%	$97.1603	$97.16	$97.15	$97.20
Purchase #3	$163.89	6.813%	$175.0558	$175.06	$175.05	$175.10
Purchase #4	$117.89	11.499%	$131.4462	$131.45	$131.45	$131.40
Purchase #5	$141.57	3.148%	$146.0266	$146.03	$146.05	$146.00
Purchase #6	$184.97	13.475%	$209.8947	$209.89	$209.90	$209.90
Purchase #7	$140.27	6.469%	$149.3441	$149.34	$149.35	$149.30
7 purchase totals =	$868.01		$940.8138	$940.82	$940.85	$940.80