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	$28.92	8.430%	$31.358	$31.36	$31.35	$31.40
Purchase #2	$149.79	10.812%	$165.9853	$165.99	$166.00	$166.00
Purchase #3	$206.89	8.213%	$223.8819	$223.88	$223.90	$223.90
Purchase #4	$21.50	6.533%	$22.9046	$22.90	$22.90	$22.90
Purchase #5	$103.90	5.392%	$109.5023	$109.50	$109.50	$109.50
Purchase #6	$206.69	6.271%	$219.6515	$219.65	$219.65	$219.70
Purchase #7	$152.36	10.859%	$168.9048	$168.90	$168.90	$168.90
7 purchase totals =	$870.05		$942.1884	$942.18	$942.20	$942.30