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	$136.46	10.464%	$150.7392	$150.74	$150.75	$150.70
Purchase #2	$71.32	12.552%	$80.2721	$80.27	$80.25	$80.30
Purchase #3	$243.79	3.282%	$251.7912	$251.79	$251.80	$251.80
Purchase #4	$194.37	6.271%	$206.5589	$206.56	$206.55	$206.60
Purchase #5	$81.62	11.260%	$90.8104	$90.81	$90.80	$90.80
Purchase #6	$26.30	12.224%	$29.5149	$29.51	$29.50	$29.50
Purchase #7	$216.46	11.111%	$240.5109	$240.51	$240.50	$240.50
7 purchase totals =	$970.32		$1,050.1976	$1,050.19	$1,050.15	$1,050.20