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	$109.36	10.530%	$120.8756	$120.88	$120.90	$120.90
Purchase #2	$33.98	12.166%	$38.114	$38.11	$38.10	$38.10
Purchase #3	$143.85	4.436%	$150.2312	$150.23	$150.25	$150.20
Purchase #4	$31.39	13.201%	$35.5338	$35.53	$35.55	$35.50
Purchase #5	$103.64	13.703%	$117.8418	$117.84	$117.85	$117.80
Purchase #6	$190.82	7.699%	$205.5112	$205.51	$205.50	$205.50
Purchase #7	$73.82	12.359%	$82.9434	$82.94	$82.95	$82.90
7 purchase totals =	$686.86		$751.0510	$751.04	$751.10	$750.90