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	$186.26	3.606%	$192.9765	$192.98	$193.00	$193.00
Purchase #2	$152.45	7.837%	$164.3975	$164.40	$164.40	$164.40
Purchase #3	$228.66	9.143%	$249.5664	$249.57	$249.55	$249.60
Purchase #4	$37.72	8.700%	$41.0016	$41.00	$41.00	$41.00
Purchase #5	$18.40	11.405%	$20.4985	$20.50	$20.50	$20.50
Purchase #6	$199.69	11.340%	$222.3348	$222.33	$222.35	$222.30
Purchase #7	$216.83	12.454%	$243.834	$243.83	$243.85	$243.80
7 purchase totals =	$1,040.01		$1,134.6093	$1,134.61	$1,134.65	$1,134.60