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	$88.83	13.487%	$100.8105	$100.81	$100.80	$100.80
Purchase #2	$108.53	4.711%	$113.6428	$113.64	$113.65	$113.60
Purchase #3	$28.88	12.104%	$32.3756	$32.38	$32.40	$32.40
Purchase #4	$171.89	6.398%	$182.8875	$182.89	$182.90	$182.90
Purchase #5	$84.40	8.361%	$91.4567	$91.46	$91.45	$91.50
Purchase #6	$106.57	11.134%	$118.4355	$118.44	$118.45	$118.40
Purchase #7	$190.54	9.498%	$208.6375	$208.64	$208.65	$208.60
7 purchase totals =	$779.64		$848.2461	$848.26	$848.30	$848.20