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	$68.50	7.328%	$73.5197	$73.52	$73.50	$73.50
Purchase #2	$36.94	11.797%	$41.2978	$41.30	$41.30	$41.30
Purchase #3	$14.30	5.180%	$15.0407	$15.04	$15.05	$15.00
Purchase #4	$223.71	12.104%	$250.7879	$250.79	$250.80	$250.80
Purchase #5	$78.79	8.300%	$85.3296	$85.33	$85.35	$85.30
Purchase #6	$27.61	10.287%	$30.4502	$30.45	$30.45	$30.50
Purchase #7	$162.95	5.201%	$171.425	$171.43	$171.45	$171.40
7 purchase totals =	$612.80		$667.8509	$667.86	$667.90	$667.80