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	$40.72	6.286%	$43.2797	$43.28	$43.30	$43.30
Purchase #2	$191.89	9.231%	$209.6034	$209.60	$209.60	$209.60
Purchase #3	$177.57	7.781%	$191.3867	$191.39	$191.40	$191.40
Purchase #4	$133.76	12.499%	$150.4787	$150.48	$150.50	$150.50
Purchase #5	$93.66	6.380%	$99.6355	$99.64	$99.65	$99.60
Purchase #6	$144.53	13.757%	$164.413	$164.41	$164.40	$164.40
Purchase #7	$189.27	6.533%	$201.635	$201.64	$201.65	$201.60
7 purchase totals =	$971.40		$1,060.4320	$1,060.44	$1,060.50	$1,060.40