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	$99.38	8.817%	$108.1423	$108.14	$108.15	$108.10
Purchase #2	$133.94	6.216%	$142.2657	$142.27	$142.25	$142.30
Purchase #3	$53.43	6.543%	$56.9259	$56.93	$56.95	$56.90
Purchase #4	$119.96	13.691%	$136.3837	$136.38	$136.40	$136.40
Purchase #5	$187.98	13.419%	$213.205	$213.21	$213.20	$213.20
Purchase #6	$141.25	3.581%	$146.3082	$146.31	$146.30	$146.30
Purchase #7	$90.59	8.518%	$98.3065	$98.31	$98.30	$98.30
7 purchase totals =	$826.53		$901.5373	$901.55	$901.55	$901.50