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	$234.58	3.357%	$242.4549	$242.45	$242.45	$242.50
Purchase #2	$245.41	11.292%	$273.1217	$273.12	$273.10	$273.10
Purchase #3	$79.54	6.225%	$84.4914	$84.49	$84.50	$84.50
Purchase #4	$83.67	8.524%	$90.802	$90.80	$90.80	$90.80
Purchase #5	$61.82	9.243%	$67.534	$67.53	$67.55	$67.50
Purchase #6	$163.97	9.590%	$179.6947	$179.69	$179.70	$179.70
Purchase #7	$99.55	5.271%	$104.7973	$104.80	$104.80	$104.80
7 purchase totals =	$968.54		$1,042.8960	$1,042.88	$1,042.90	$1,042.90