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	$102.38	7.170%	$109.7206	$109.72	$109.70	$109.70
Purchase #2	$243.92	7.580%	$262.4091	$262.41	$262.40	$262.40
Purchase #3	$144.50	5.112%	$151.8868	$151.89	$151.90	$151.90
Purchase #4	$52.43	11.214%	$58.3095	$58.31	$58.30	$58.30
Purchase #5	$7.48	5.753%	$7.9103	$7.91	$7.90	$7.90
Purchase #6	$95.59	8.705%	$103.9111	$103.91	$103.90	$103.90
Purchase #7	$177.51	4.159%	$184.8926	$184.89	$184.90	$184.90
7 purchase totals =	$823.81		$879.0400	$879.04	$879.00	$879.00