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	$21.34	3.600%	$22.1082	$22.11	$22.10	$22.10
Purchase #2	$233.56	11.542%	$260.5175	$260.52	$260.50	$260.50
Purchase #3	$97.54	11.788%	$109.038	$109.04	$109.05	$109.00
Purchase #4	$142.50	3.737%	$147.8252	$147.83	$147.85	$147.80
Purchase #5	$144.67	5.457%	$152.5646	$152.56	$152.55	$152.60
Purchase #6	$73.67	13.807%	$83.8416	$83.84	$83.85	$83.80
Purchase #7	$244.41	9.409%	$267.4065	$267.41	$267.40	$267.40
7 purchase totals =	$957.69		$1,043.3016	$1,043.31	$1,043.30	$1,043.20