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	$84.36	13.610%	$95.8414	$95.84	$95.85	$95.80
Purchase #2	$245.65	10.514%	$271.4776	$271.48	$271.50	$271.50
Purchase #3	$150.52	11.710%	$168.1459	$168.15	$168.15	$168.10
Purchase #4	$67.80	7.467%	$72.8626	$72.86	$72.85	$72.90
Purchase #5	$85.47	7.526%	$91.9025	$91.90	$91.90	$91.90
Purchase #6	$16.33	3.688%	$16.9323	$16.93	$16.95	$16.90
Purchase #7	$241.96	11.713%	$270.3008	$270.30	$270.30	$270.30
7 purchase totals =	$892.09		$987.4631	$987.46	$987.50	$987.40