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	$121.25	12.285%	$136.1456	$136.15	$136.15	$136.10
Purchase #2	$211.90	13.687%	$240.9028	$240.90	$240.90	$240.90
Purchase #3	$249.47	8.263%	$270.0837	$270.08	$270.10	$270.10
Purchase #4	$207.75	5.194%	$218.5405	$218.54	$218.55	$218.50
Purchase #5	$70.49	11.402%	$78.5273	$78.53	$78.55	$78.50
Purchase #6	$97.34	11.228%	$108.2693	$108.27	$108.25	$108.30
Purchase #7	$82.38	7.681%	$88.7076	$88.71	$88.70	$88.70
7 purchase totals =	$1,040.58		$1,141.1768	$1,141.18	$1,141.20	$1,141.10