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	$115.77	7.833%	$124.8383	$124.84	$124.85	$124.80
Purchase #2	$90.36	10.684%	$100.0141	$100.01	$100.00	$100.00
Purchase #3	$96.77	13.585%	$109.9162	$109.92	$109.90	$109.90
Purchase #4	$248.33	10.669%	$274.8243	$274.82	$274.80	$274.80
Purchase #5	$71.32	6.577%	$76.0107	$76.01	$76.00	$76.00
Purchase #6	$118.40	4.471%	$123.6937	$123.69	$123.70	$123.70
Purchase #7	$39.36	6.494%	$41.916	$41.92	$41.90	$41.90
7 purchase totals =	$780.31		$851.2133	$851.21	$851.15	$851.10