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	$35.58	3.285%	$36.7488	$36.75	$36.75	$36.70
Purchase #2	$85.54	7.399%	$91.8691	$91.87	$91.85	$91.90
Purchase #3	$74.51	4.721%	$78.0276	$78.03	$78.05	$78.00
Purchase #4	$6.69	9.729%	$7.3409	$7.34	$7.35	$7.30
Purchase #5	$37.90	13.718%	$43.0991	$43.10	$43.10	$43.10
Purchase #6	$166.38	5.403%	$175.3695	$175.37	$175.35	$175.40
Purchase #7	$203.76	12.142%	$228.5005	$228.50	$228.50	$228.50
7 purchase totals =	$610.36		$660.9555	$660.96	$660.95	$660.90