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	$25.72	10.109%	$28.32	$28.32	$28.30	$28.30
Purchase #2	$188.62	13.154%	$213.4311	$213.43	$213.45	$213.40
Purchase #3	$178.56	9.861%	$196.1678	$196.17	$196.15	$196.20
Purchase #4	$199.29	3.659%	$206.582	$206.58	$206.60	$206.60
Purchase #5	$43.28	3.484%	$44.7879	$44.79	$44.80	$44.80
Purchase #6	$188.54	12.336%	$211.7983	$211.80	$211.80	$211.80
Purchase #7	$182.77	3.872%	$189.8469	$189.85	$189.85	$189.80
7 purchase totals =	$1,006.78		$1,090.9340	$1,090.94	$1,090.95	$1,090.90