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	$77.98	5.409%	$82.1979	$82.20	$82.20	$82.20
Purchase #2	$115.83	11.402%	$129.0369	$129.04	$129.05	$129.00
Purchase #3	$181.27	10.338%	$200.0097	$200.01	$200.00	$200.00
Purchase #4	$86.44	3.362%	$89.3461	$89.35	$89.35	$89.30
Purchase #5	$241.90	8.266%	$261.8955	$261.90	$261.90	$261.90
Purchase #6	$219.69	13.747%	$249.8908	$249.89	$249.90	$249.90
Purchase #7	$66.84	6.738%	$71.3437	$71.34	$71.35	$71.30
7 purchase totals =	$989.95		$1,083.7206	$1,083.73	$1,083.75	$1,083.60