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	$189.64	7.348%	$203.5747	$203.57	$203.55	$203.60
Purchase #2	$37.73	12.809%	$42.5628	$42.56	$42.55	$42.60
Purchase #3	$130.32	13.445%	$147.8415	$147.84	$147.85	$147.80
Purchase #4	$151.44	3.610%	$156.907	$156.91	$156.90	$156.90
Purchase #5	$56.83	12.324%	$63.8337	$63.83	$63.85	$63.80
Purchase #6	$189.50	3.388%	$195.9203	$195.92	$195.90	$195.90
Purchase #7	$44.37	4.311%	$46.2828	$46.28	$46.30	$46.30
7 purchase totals =	$799.83		$856.9228	$856.91	$856.90	$856.90