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	$189.39	12.845%	$213.7171	$213.72	$213.70	$213.70
Purchase #2	$178.88	12.319%	$200.9162	$200.92	$200.90	$200.90
Purchase #3	$162.34	11.223%	$180.5594	$180.56	$180.55	$180.60
Purchase #4	$5.53	7.186%	$5.9274	$5.93	$5.95	$5.90
Purchase #5	$167.81	10.391%	$185.2471	$185.25	$185.25	$185.20
Purchase #6	$57.54	10.326%	$63.4816	$63.48	$63.50	$63.50
Purchase #7	$38.56	7.165%	$41.3228	$41.32	$41.30	$41.30
7 purchase totals =	$800.05		$891.1716	$891.18	$891.15	$891.10