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	$248.57	7.780%	$267.9087	$267.91	$267.90	$267.90
Purchase #2	$153.76	11.622%	$171.63	$171.63	$171.65	$171.60
Purchase #3	$244.87	11.593%	$273.2578	$273.26	$273.25	$273.30
Purchase #4	$6.77	11.165%	$7.5259	$7.53	$7.55	$7.50
Purchase #5	$63.76	13.311%	$72.2471	$72.25	$72.25	$72.20
Purchase #6	$133.53	13.335%	$151.3362	$151.34	$151.35	$151.30
Purchase #7	$39.34	5.459%	$41.4876	$41.49	$41.50	$41.50
7 purchase totals =	$890.60		$985.3933	$985.41	$985.45	$985.30