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	$167.94	10.623%	$185.7803	$185.78	$185.80	$185.80
Purchase #2	$221.85	5.120%	$233.2087	$233.21	$233.20	$233.20
Purchase #3	$132.37	5.257%	$139.3287	$139.33	$139.35	$139.30
Purchase #4	$67.43	5.732%	$71.2951	$71.30	$71.30	$71.30
Purchase #5	$141.89	7.482%	$152.5062	$152.51	$152.50	$152.50
Purchase #6	$246.77	12.618%	$277.9074	$277.91	$277.90	$277.90
Purchase #7	$168.48	6.549%	$179.5138	$179.51	$179.50	$179.50
7 purchase totals =	$1,146.73		$1,239.5402	$1,239.55	$1,239.55	$1,239.50