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	$187.34	6.127%	$198.8183	$198.82	$198.80	$198.80
Purchase #2	$28.31	7.783%	$30.5134	$30.51	$30.50	$30.50
Purchase #3	$98.49	11.166%	$109.4874	$109.49	$109.50	$109.50
Purchase #4	$149.59	3.865%	$155.3717	$155.37	$155.35	$155.40
Purchase #5	$96.73	3.696%	$100.3051	$100.31	$100.30	$100.30
Purchase #6	$101.35	9.221%	$110.6955	$110.70	$110.70	$110.70
Purchase #7	$187.40	6.809%	$200.1601	$200.16	$200.15	$200.20
7 purchase totals =	$849.21		$905.3515	$905.36	$905.30	$905.40