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	$103.46	7.148%	$110.8553	$110.86	$110.85	$110.90
Purchase #2	$154.79	3.484%	$160.1829	$160.18	$160.20	$160.20
Purchase #3	$79.60	4.874%	$83.4797	$83.48	$83.50	$83.50
Purchase #4	$134.51	6.192%	$142.8389	$142.84	$142.85	$142.80
Purchase #5	$230.86	10.104%	$254.1861	$254.19	$254.20	$254.20
Purchase #6	$86.48	3.298%	$89.3321	$89.33	$89.35	$89.30
Purchase #7	$35.33	4.435%	$36.8969	$36.90	$36.90	$36.90
7 purchase totals =	$825.03		$877.7719	$877.78	$877.85	$877.80