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	$135.48	3.184%	$139.7937	$139.79	$139.80	$139.80
Purchase #2	$75.40	13.468%	$85.5549	$85.55	$85.55	$85.60
Purchase #3	$198.86	11.543%	$221.8144	$221.81	$221.80	$221.80
Purchase #4	$85.67	5.373%	$90.273	$90.27	$90.25	$90.30
Purchase #5	$147.84	12.363%	$166.1175	$166.12	$166.10	$166.10
Purchase #6	$191.25	3.815%	$198.5462	$198.55	$198.55	$198.50
Purchase #7	$125.89	11.746%	$140.677	$140.68	$140.70	$140.70
7 purchase totals =	$960.39		$1,042.7767	$1,042.77	$1,042.75	$1,042.80