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	$190.85	9.556%	$209.0876	$209.09	$209.10	$209.10
Purchase #2	$150.48	4.275%	$156.913	$156.91	$156.90	$156.90
Purchase #3	$182.54	7.521%	$196.2688	$196.27	$196.25	$196.30
Purchase #4	$122.32	10.825%	$135.5611	$135.56	$135.55	$135.60
Purchase #5	$86.36	6.270%	$91.7748	$91.77	$91.75	$91.80
Purchase #6	$87.77	10.441%	$96.9341	$96.93	$96.95	$96.90
Purchase #7	$195.50	4.443%	$204.1861	$204.19	$204.20	$204.20
7 purchase totals =	$1,015.82		$1,090.7255	$1,090.72	$1,090.70	$1,090.80