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	$10.39	13.528%	$11.7956	$11.80	$11.80	$11.80
Purchase #2	$185.65	4.133%	$193.3229	$193.32	$193.30	$193.30
Purchase #3	$82.75	11.590%	$92.3407	$92.34	$92.35	$92.30
Purchase #4	$63.54	6.849%	$67.8919	$67.89	$67.90	$67.90
Purchase #5	$196.30	13.622%	$223.04	$223.04	$223.05	$223.00
Purchase #6	$125.39	13.224%	$141.9716	$141.97	$141.95	$142.00
Purchase #7	$30.39	4.854%	$31.8651	$31.87	$31.85	$31.90
7 purchase totals =	$694.41		$762.2278	$762.23	$762.20	$762.20