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	$91.43	12.192%	$102.5771	$102.58	$102.60	$102.60
Purchase #2	$44.44	3.287%	$45.9007	$45.90	$45.90	$45.90
Purchase #3	$10.54	9.637%	$11.5557	$11.56	$11.55	$11.60
Purchase #4	$190.32	4.710%	$199.2841	$199.28	$199.30	$199.30
Purchase #5	$209.32	3.391%	$216.418	$216.42	$216.40	$216.40
Purchase #6	$234.62	6.682%	$250.2973	$250.30	$250.30	$250.30
Purchase #7	$35.68	4.322%	$37.2221	$37.22	$37.20	$37.20
7 purchase totals =	$816.35		$863.2550	$863.26	$863.25	$863.30