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	$191.40	3.600%	$198.2904	$198.29	$198.30	$198.30
Purchase #2	$247.53	6.770%	$264.2878	$264.29	$264.30	$264.30
Purchase #3	$156.90	4.409%	$163.8177	$163.82	$163.80	$163.80
Purchase #4	$58.89	3.505%	$60.9541	$60.95	$60.95	$61.00
Purchase #5	$82.54	13.709%	$93.8554	$93.86	$93.85	$93.90
Purchase #6	$187.76	6.777%	$200.4845	$200.48	$200.50	$200.50
Purchase #7	$19.86	7.345%	$21.3187	$21.32	$21.30	$21.30
7 purchase totals =	$944.88		$1,003.0086	$1,003.01	$1,003.00	$1,003.10