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	$134.47	12.220%	$150.9022	$150.90	$150.90	$150.90
Purchase #2	$89.74	11.608%	$100.157	$100.16	$100.15	$100.20
Purchase #3	$206.35	3.782%	$214.1542	$214.15	$214.15	$214.20
Purchase #4	$213.78	8.707%	$232.3938	$232.39	$232.40	$232.40
Purchase #5	$90.46	13.352%	$102.5382	$102.54	$102.55	$102.50
Purchase #6	$42.35	8.360%	$45.8905	$45.89	$45.90	$45.90
Purchase #7	$30.49	3.192%	$31.4632	$31.46	$31.45	$31.50
7 purchase totals =	$807.64		$877.4991	$877.49	$877.50	$877.60