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	$170.56	13.679%	$193.8909	$193.89	$193.90	$193.90
Purchase #2	$200.84	10.805%	$222.5408	$222.54	$222.55	$222.50
Purchase #3	$237.72	11.386%	$264.7868	$264.79	$264.80	$264.80
Purchase #4	$43.59	8.610%	$47.3431	$47.34	$47.35	$47.30
Purchase #5	$128.30	8.862%	$139.6699	$139.67	$139.65	$139.70
Purchase #6	$80.90	8.736%	$87.9674	$87.97	$87.95	$88.00
Purchase #7	$88.40	6.374%	$94.0346	$94.03	$94.05	$94.00
7 purchase totals =	$950.31		$1,050.2335	$1,050.23	$1,050.25	$1,050.20