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	$78.54	3.427%	$81.2316	$81.23	$81.25	$81.20
Purchase #2	$184.71	6.270%	$196.2913	$196.29	$196.30	$196.30
Purchase #3	$81.25	10.337%	$89.6488	$89.65	$89.65	$89.60
Purchase #4	$131.77	13.334%	$149.3402	$149.34	$149.35	$149.30
Purchase #5	$159.37	12.398%	$179.1287	$179.13	$179.15	$179.10
Purchase #6	$82.41	5.279%	$86.7604	$86.76	$86.75	$86.80
Purchase #7	$23.34	8.871%	$25.4105	$25.41	$25.40	$25.40
7 purchase totals =	$741.39		$807.8115	$807.81	$807.85	$807.70