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	$237.28	4.236%	$247.3312	$247.33	$247.35	$247.30
Purchase #2	$233.88	4.129%	$243.5369	$243.54	$243.55	$243.50
Purchase #3	$28.74	7.691%	$30.9504	$30.95	$30.95	$31.00
Purchase #4	$87.81	13.841%	$99.9638	$99.96	$99.95	$100.00
Purchase #5	$130.94	12.598%	$147.4358	$147.44	$147.45	$147.40
Purchase #6	$250.63	8.131%	$271.0087	$271.01	$271.00	$271.00
Purchase #7	$131.37	6.254%	$139.5859	$139.59	$139.60	$139.60
7 purchase totals =	$1,100.65		$1,179.8127	$1,179.82	$1,179.85	$1,179.80