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	$31.33	3.769%	$32.5108	$32.51	$32.50	$32.50
Purchase #2	$54.82	3.277%	$56.6165	$56.62	$56.60	$56.60
Purchase #3	$121.78	12.783%	$137.3471	$137.35	$137.35	$137.30
Purchase #4	$121.93	3.273%	$125.9208	$125.92	$125.90	$125.90
Purchase #5	$212.29	7.814%	$228.8783	$228.88	$228.90	$228.90
Purchase #6	$85.96	6.130%	$91.2293	$91.23	$91.25	$91.20
Purchase #7	$33.33	11.632%	$37.2069	$37.21	$37.20	$37.20
7 purchase totals =	$661.44		$709.7097	$709.72	$709.70	$709.60