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	$84.84	6.215%	$90.1128	$90.11	$90.10	$90.10
Purchase #2	$165.53	8.775%	$180.0553	$180.06	$180.05	$180.10
Purchase #3	$84.55	7.610%	$90.9843	$90.98	$91.00	$91.00
Purchase #4	$73.99	11.646%	$82.6069	$82.61	$82.60	$82.60
Purchase #5	$66.99	6.822%	$71.5601	$71.56	$71.55	$71.60
Purchase #6	$128.47	12.208%	$144.1536	$144.15	$144.15	$144.20
Purchase #7	$192.55	12.426%	$216.4763	$216.48	$216.50	$216.50
7 purchase totals =	$796.92		$875.9493	$875.95	$875.95	$876.10