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	$86.96	13.863%	$99.0153	$99.02	$99.00	$99.00
Purchase #2	$98.64	12.761%	$111.2275	$111.23	$111.25	$111.20
Purchase #3	$225.72	11.381%	$251.4092	$251.41	$251.40	$251.40
Purchase #4	$84.99	5.283%	$89.48	$89.48	$89.50	$89.50
Purchase #5	$91.36	9.143%	$99.713	$99.71	$99.70	$99.70
Purchase #6	$101.67	8.629%	$110.4431	$110.44	$110.45	$110.40
Purchase #7	$167.34	4.864%	$175.4794	$175.48	$175.50	$175.50
7 purchase totals =	$856.68		$936.7675	$936.77	$936.80	$936.70