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	$140.56	4.498%	$146.8824	$146.88	$146.90	$146.90
Purchase #2	$30.48	3.364%	$31.5053	$31.51	$31.50	$31.50
Purchase #3	$155.36	10.137%	$171.1088	$171.11	$171.10	$171.10
Purchase #4	$80.28	10.676%	$88.8507	$88.85	$88.85	$88.90
Purchase #5	$115.87	8.128%	$125.2879	$125.29	$125.30	$125.30
Purchase #6	$127.40	10.340%	$140.5732	$140.57	$140.55	$140.60
Purchase #7	$100.56	3.246%	$103.8242	$103.82	$103.80	$103.80
7 purchase totals =	$750.51		$808.0325	$808.03	$808.00	$808.10