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	$82.73	8.237%	$89.5445	$89.54	$89.55	$89.50
Purchase #2	$78.76	11.814%	$88.0647	$88.06	$88.05	$88.10
Purchase #3	$246.66	8.857%	$268.5067	$268.51	$268.50	$268.50
Purchase #4	$246.64	4.807%	$258.496	$258.50	$258.50	$258.50
Purchase #5	$66.57	4.417%	$69.5104	$69.51	$69.50	$69.50
Purchase #6	$166.90	7.477%	$179.3791	$179.38	$179.40	$179.40
Purchase #7	$218.32	8.214%	$236.2528	$236.25	$236.25	$236.30
7 purchase totals =	$1,106.58		$1,189.7542	$1,189.75	$1,189.75	$1,189.80