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	$29.91	10.545%	$33.064	$33.06	$33.05	$33.10
Purchase #2	$137.74	9.226%	$150.4479	$150.45	$150.45	$150.40
Purchase #3	$83.69	13.403%	$94.907	$94.91	$94.90	$94.90
Purchase #4	$96.84	4.115%	$100.825	$100.83	$100.85	$100.80
Purchase #5	$5.48	6.626%	$5.8431	$5.84	$5.85	$5.80
Purchase #6	$65.57	8.807%	$71.3447	$71.34	$71.35	$71.30
Purchase #7	$131.46	7.614%	$141.4694	$141.47	$141.45	$141.50
7 purchase totals =	$550.69		$597.9011	$597.90	$597.90	$597.80